Some of this information is cited, some of it isn't. There are claims that are common knowledge for people familiar with these instruments and there are claims that I've gathered through research and first-hand experience. 

Brand name breakdowns for both manufacturers can be found on my page

https://www.stlamateurluthier.com/2019/06/vintage-chicago-built-guitars-brand.html

Kay 

Symbols

• "K-#### ####"
• Stamped inside the body on the back
• Numbers following the "K" are the model number of the instrument
• Remaining 4 numbers are meaningless and likely batch related
• "L#### ####"
• Stamped inside the body on the back
• Unknown meaning but likely related to the batch
• Commonly (and wrongly) attributed to be a model number
• "N#", "P#", "B#"
• Stamped inside the body on the back
• Unknown meanings
• N numbers can go up to 15. [4]
• P numbers can go up to 7. [3]
• B numbers can go up to 10. [5]
• N and P numbers can occur together
• B and N numbers can occur together

Headstock Variants

[1940s] Rounded point, smaller at the
top, very Harmony-esque

[1940s] Sharp point, steep angle

[1960s] Sharp point, shallow angle

[1960s] Rounded 3 point 

Fretboard

• Brazilian Rosewood
• Associated with high end instruments
• Lower end archtops could be seen with it up until the 60s
• Indian Rosewood
• Became the economic choice in the 1960s
• Maple
• Painted black or ebonized
• Red-dyed plywood boards appear on 1960s archtops
• Lacquered maple boards also appear on 1960s archtops
• Walnut
• Appeared in the 1940s
• Claimed in a couple 1960's catalogs



1961 Montgomery Ward catalog [1]



1958 Silvertone catalog [2]

• During the 50s, a mystery wood appeared on flat tops

• That stock of wood remained in some acoustic bridges into the late 1960s
• I've seen people claim its rosewood, walnut, or mahogany

• Position dots
• 3/8" pearloid or white dots in a single line pattern appeared in the 1960s
• 7/32" mother of pearl dots at latest in the 1950s
• 3/16" white dots in an alternating 1 and 2 dot pattern were common prior to 1960
• Some painted inlays can be found like the K1160 "music note" guitar.

Body

• Known for laminated woods, advertised as "crack-proof"
• Acoustics
• Laminated mahogany back and sides often have a solid spruce top
• Plywood back and sides often have a plywood top
• Solid body

Neck

• 1940s saw the use of some mahogany
• Most commonly poplar with grafted headstock wings

Pickups

• Some built by DeArmond, some reportedly built in-house

Harmony

Symbols

• "F-##", "S-##"
• Denotes Fall or Spring
• The number is the year that the instrument was built. ex: 19##
• Sometimes followed by a letter with an unknown meaning
• "Made in USA" appears underneath it
• ####H####
• Preceding numbers are likely a batch number
• Following numbers are the model number of the instrument
• Carved Top
• Printed in red ink, indicates a high end model with a carved (rather than heat pressed) arch top

Headstock Variants

[1940s] Rounded, narrow headstock

[1950s] Typical Harmony, rounded top

[1930s] Rounded, significantly smaller at the bottom

Fretboard

• Brazilian Rosewood
• Continued to appear on mid to high-end models far into the 1960s
• Ebonized
• Fairly common on low-end models
• Brittle and prone to cracking and chipping
• Position dots
• 3/16" white dots in an alternating 1 and 2 dot pattern in the 1930s
• Commonly painted using ornate stencils

Body

• Known for using solid woods
• Acoustics
• Solid mahogany and solid spruce
• Solid birch on low end models
• Electrics
• 
  

Pickups

• DeArmond gold foils

Sources

[1] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1961airline_ward_page02&cat_1961airline_ward_page02

[2] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1958silvertone_sears_page03&cat_1958silvertone_sears_page03
[3] https://reverb.com/item/16020800-silvertone-p7-archtop-jazzbox-from-the-early-1960s
[4] https://reverb.com/item/1282372-kay-n-15-1950s-1960s-sunburst
[5] https://reverb.com/item/25986397-kay-b10-1960s-brown-sunburst

1930s Kay with no steel bar and a new hole drilled just under the fingerboard

Why is this needed?

Old guitars were often built with a steel bar in the neck to help counteract the force of the string tension and prevent the neck from developing a bow. Acoustic strings can put up to 200lbs of force on a guitar and even maple can only resist that pull for so long. So the adjustable truss rod system was developed to reinforce necks and allow for an adjustable bow which has probably been one of the greatest advancements in guitar building. They were more expensive to install and make than a steel bar so often lower end guitars find themselves with steel or sometimes nothing (especially common in the 1940s because of the war).

Often times people will sand the fretboard flat again (removing more material from the ends than the center) and refret but this is only a band-aid. In some cases, sanding the fretboard removes patina, dyes, or physical wear that fit the instrument and make it unique. The best method for preserving the fretboard (besides a compression fret) is to remove the fretboard, install reinforcements, and reglue it. This is expensive as it takes time and care plus finish touchups afterwards. That often means that old inexpensive guitars are not worth sending through this process and end up unplayable. 

I seek to change that by creating a more economical method

What do you need?

• The guitar in question must not already have a steel rod or truss rod installed
• A 15" or longer spade drill bit
• A corded drill
• A jig to clamp the neck securely and also add back bow

How does it work?

First, I begin by removing the neck using the typical method of steam and clean it of excess glue

Second, I place the neck into my jig that holds it steady at the heel and at the peghead and begin turning my turnbuckle/neck-cradle which forces the middle of the neck upwards and into a backbow

Then, I put a 15" 3/8" drill bit into a corded (you'll want the constant power) drill, line it up, and begin drilling until I have reached just past the 1st fret

• I set magnets on top of the fretboard which glide towards the center of the drill bit and help let me know if I'm veering to the left or right
• I also use a flashlight and look into the hole periodically to make sure I'm going straight and not up into the board or down 

Finally, I get my carbon fiber inserts (recently been using a 3/8x3/8 bar), check the fit, pour glue down the channel, and gently nudge the carbon fiber in using a mallet. Saw the excess off so you're flush with the dovetail

This operation was done and the fret dots popped out
allowing me to see the channel I had cut.
Note the ebonized board which would not have taken
a planing and looked the same

Results & Improvements

It takes me about an hour to drill a hole through the neck, depending on the material, and much more care is needed for thinner neck profiles. The ideal neck would be a V or U shape (to prevent from accidentally drilling out through the neck) with a fretboard which is harder than the neck wood (to discourage the bit from wandering into the board)

I've had varied success depending on the neck/fretboard wood's rigidity and how much backbow I've put into the neck before drilling. I've also used this method in conjunction with a heat-press and had good results. 

I've dabbled in using this method to install truss rods and haven't quite gotten a successful result yet.

What I've learned

• If the neck already has a steel bar, they are not easy to remove through the heel
• Force the neck into a backbow (not straight!) before drilling. A larger bow is needed for softer woods
• Work slowly

The strangest instrument I've come across

But built pretty well for being a DIY job.

This is a 1920s Bruno & Sons No. 200 "Vernon" banjo neck mounted on a 1950s Kay tenor archtop body. The neck is birch with an ebonized maple fretboard that has mother of pearl inlays in it. I reinforced it with carbon fiber to help keep it straight but there is only so much it could do. The body has had a couple impacts and some were repaired with a really strong glue that I could not break with heat. The tailpiece is a tenor tailpiece that has been slotted for accepting banjo string loops. 

Note the pseudo-heel that was made from the neck. It screws to the neck and screws to the neck block.

Black clay inserts are pressed into the ebonized maple fretboard

They disguise screws

Two screws go into the neck block while a makeshift dovetail helps lock it in place.

Pearl fleur-de-lis hidden under the black paint

Original Kay tuners chopped and carved to fit on the neck

For sale here:
https://reverb.com/item/25829831-vintage-kay-archtop-bruno-banjo-conversion

To preface this, I don't believe that Tony Rizzo intended on scamming me but rather that he simply found himself in a situation where he made a mistake and he didn't want to face the consequences. I learned a valuable lesson about always obtaining good photo evidence even if the person seems trustworthy because of their role; people don't like to admit they are wrong.

Anthony "Tony" Rizzo is a moderator of the Awesome Cheap Guitars Facebook group and fancies vintage Japanese guitars. If you ever get the chance to

He resides at:
818 East Washington St.
Joliet IL 60433

The situation:

We agreed to a trade; my green Greco beatle bass for his sunburst Winston electric 12 string. My instrument was packed in a full sized box with care and his instrument was packaged with less care in a very small box. I confronted him and discussed working something out and he blocked me leaving me with a broken instrument.

His mistakes

1. He left it strung to tension in the middle of a hot September
2. He put it in a small box with insufficient padding
3. And he didn't purchase shipping insurance

My mistakes

1. I didn't take photographic evidence of the neck bow
2. I didn't notice that he did not purchase shipping insurance
3. I trusted that a 51 year old man who runs a guitar Facebook group would be trustworthy

I raised attention to this in the group in September and was ignored by moderation and received no official word about it. I contacted the page admins again in October and was similarly ignored.

After months of giving up, I made another post in March trying to follow up on the case and FINALLY after 6 months I received a reply by Jack Rainwater saying that he didn't think my evidence was sufficient enough and so he did not respond to my earlier messages. I was furious and Tony Rizzo made disparaging comments towards me but kept me blocked so that I was unable to see and respond to them. People used the logic that because I did not respond to his rebuttals (because I could not see them), I was a scammer. Overall it was a complete disaster and I was not thinking straight because of my sheer frustration and how Tony's friends accused me of being a liar and scammer so I left the group.

People who did question Tony and why he had continually kept me blocked instead of trying to reach a civil conclusion were temporarily muted in the group. While this gentlemen below was a little more aggressive than I was, I think his point still stands.

Finally

I fixed his guitar up after leaving it sitting on a shelf for months because it irritated me so much to think about. It needed a new truss rod because the old truss rod was not strong enough to get the warp out of the neck and the neck was twisted. The separating body plys are unfortunate but appear to be stable and so I left them alone. I then had to plane the fretboard, refret it, and restring it. Its a decent guitar but nowhere near as good as the bass I traded him

I know not all of my evidence is concrete and I've learned a lot from this. I just wanted to make sure people know what he did

This is my attempt to try and consolidate some knowledge about the tailpieces that appear on old acoustic guitars from the mid century. I am mostly focusing on lower end instruments from factories like Kay, Harmony, and Regal and specifically their guitars.

No.
Appears On:
Years:
Construction: 

Screws:
Mounting Face: 

Mid Face:

Front Face:

Flattop Tailpieces

[8]

No. 11356
Appears On: Wurlitzer-branded instruments
Years: Early 1900s
Construction: Stamped, nickel-plated brass
Screws:3
Mounting Face: Spade shaped

Mid Face: Hourglass figure with 3 distinct curves per side

Front Face: Folded over for string mounting

[5]

No. 12R5186
Appears On: Sears Roebuck
Construction: Stamped, nickel plated brass

Screws: 3
Mounting Face: Spade shaped

Mid Face: Hourglass figure with 5 curves per side

Front Face: Folded over and notched for strings

[16]

No.
Appears On: Kay
Years: 1960s
Construction: Stamped, nickel plated steel 

Screws: 1
Mounting Face: 

Mid Face: 9 lines are etched into the left side, The Kay stylized 'K' is etched in the middle, and 3 diamond shapes are cut into the metal

Front Face: Sharp triangular raised portion for the strings to sit

[2]

No. 706
Appears On: Regal
Construction: Stamped, nickel plated steel
Screws: 3
Mounting Face: Spade shaped 

Mid Face: Trapezoid with center cut out

Front Face: Raised portion for strings to sit in, smooth front

[12]

No.
Appears On: Harmony
Years: 1950s-1960s
Construction: Stamped nickel plated steel

Screws: 2
Mounting Face: Two nubs, one for each screw

Mid Face: Trapezoid with raised lines and center cut out

Front Face: Raised portion for strings

[10]

No. 1711
Appears On: Harmony
Years: 1950s-1960s
Construction: Stamped nickel plated steel

Screws:3
Mounting Face: Spade shaped 

Mid Face: Trapezoid with raised lines on the edges and a 4 hole decorative cutout in the center. 

Front Face:Raised portion for the strings to sit, small convex curve

 [1]

No. 1701
Appears On: Harmony, Kay
Construction: Stamped, nickel plated steel
Screws: 3
Mounting Face: Spade shaped

Mid Face: Hourglass shape with 4 curves per side

Front Face: Raised portion for strings, serrated front

 [1]

No. 1705
Appears On: Harmony
Construction: Stamped, nickel plated steel
Screws:1
Mounting Face: Square shaped with cutout that comes to a point below the screw

Mid Face: Trapezoid with shield-esque cutout

Front Face: Raised portion for strings, comes to a point

[6]

No. 707, 6084
Appears On: Regal, Kay, Tonk Bros
Years: 1930s-1940s
Construction: Stamped, welded, nickel plated steel
Screws: 3
Mounting Face: Spade shaped

Mid Face: Trapezoid with cutout. All sides are folded over for a smooth feel and appearance

Front Face: Claw string mount is hidden by tailpiece cover.

[3]

No. 12L5190, 54
Appears On: Regal, Kay, B&J
Construction: Stamped, nickel plated steel
Screws: 3
Mounting Face: Raised portion in the center, 3 curves on each side that come to a singular point

Mid Face: Smooth, hourglass shape with a single curve for a fan-like appearance. Raised center for a beveled appearance.

Front Face: Raised portion for strings to sit with decorative rivets (?)

[11]

No.
Appears On: Harmony
Years: War time 1940s
Construction: Wood

Screws:2
Mounting Face: 

Mid Face: Elongated heart shape

Front Face: Small channel with holes for strings

 [1]

No. 1710  "Idento" tailpiece
Appears On: Harmony
Construction: Stamped, nickel plated steel 

Screws: 2
Mounting Face: Ornate, comes to a point

Mid Face: Art-deco, trapezoidal shapes.

Front Face: Removable insert for a card, intended for the owner's name. More art-deco influences.

[4]

No. 45
Appears On: B&J
Construction: Stamped, nickel plated steel
Mounting: 3 holes in a triangle formation

Screws: 3
Mounting Face: Spade shape

Mid Face: Hourglass figure with 4 curves

Front Face: Raised portion for strings to sit in. Two nubs on the front resemble Mickey Mouse's ears

Archtop Tailpieces

[1]

No. 1703, 6086
Appears On: Harmony, Kay
Construction: Stamped, welded, nickel plated steel 

Screws: 4
Mounting Face: 2 arms with 2 screw holes each

Mid Face: 2 arms

Front Face: Plain, rectangular cover with holes for the strings to go through

[6]

No. 6085
Appears On: Kay, Tonk Bros
Construction: Stamped, Riveted, nickel plated steel
Screws: 4
Mounting Face: 2 arms with 2 screw holes each

Mid Face: 2 arms

Front Face: Plain, rectangular cover with holes for the strings to go through. 4 rivets visibly mount each arm to the center portion.

[1]

No. 1735
Appears On; Harmony
Construction: Stamped, assembled nickel plated steel
Screws: 3
Mounting Face: Spade shaped

Mid Face: One bar bent into a U shape with acorn nuts on each end. Hinged

Front Face: Sliding string mount with fully enclosed holes for the ball ends of the strings to rest.

[13]

No.
Appears On:
Years:
Construction: Stamped, machined, nickel plated steel

Screws: 3
Mounting Face: Spade shaped with a strap button hole

Mid Face: Rod bent into a U shape, held in a hinge, and with acorn nuts affixed to the ends

Front Face: Floating bar with slots for the strings to go through and 3 lines cut into the top

No. "Adjustotone"
Appears On: Vega
Years: Late 1930s
Construction: ?
Screws: ?
Mounting Face: Adjustable thumb screw for changing the break angle of the strings. Trapezoidal construction

Mid Face: small art-deco cut out

Front Face: Thick block with holes for the strings

Image and Information Sources

 [1] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1940harmony_page35&cat_1940harmony_page35
[2] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1940regal_025&cat_1940regal_025
[3] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1915b_j_09&cat_1915b_j_09
[4] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1927B_J_020&cat_1927B_J_020
[5] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1902sears_006&cat_1902sears_006
[6] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1937tonk_041&cat_1937tonk_041
[7] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1939vega_005&cat_1939vega_005
[8] http://www.vintaxe.com/cgi-bin/vintaxe_viewer.pl?cat_1906wurlitzer_007&cat_1906wurlitzer_007
[9] https://www.ebay.com/itm/263632723231
[10] https://www.umanovguitars.com/store/item/1950s-harmony-1711-tailpiece/
[11] https://reverb.com/item/20921872-harmony-wood-carved-tailpiece-for-archtop-guitar-h1301-clipper-1940-rosewood
[12] https://www.ebay.com/itm/Chrome-Vintage-Stella-Silvertone-Harmony-Guitar-Tailpiece-/283440183202
[13] https://reverb.com/item/6323481-kluson-vintage-kay-harmony-short-trapeze-guitar-tailpiece
[16] http://thumb1.zeppy.io/d/l400/pict/293061655482/kay-deco-1960s-arch-top-guitar-tailpiece-silvertone-harmony-old-kraftsman-nr

This list is the culmination of research done by myself and others into the various brand names that appeared on instruments in the 20th century. Sources and more info can be found on the respective manufacturer pages. Not all of this information is mine, a lot of it I have compiled. Credits go to JediStar.com, Harmony.DeMont.com, Jake Wildwood, and more

Kay Specific Brands and Photos
Harmony Specific Brands and Photos

Brand	Distributor	Built By			Years Active	Notes
		Kay	Harmony	Regal
A. Rogers	Selmer UK		Y		1940s
Airline	Montgomery Ward	Y	Y		1958-1968
Alamo						Purchased parts from Kay
Aloha			Y
Ambassador		Y	Y
Arch Kraft	Vitak-Elsnic co	Y			1933-1937
Armstrong			Y		1940s
Barclay	Unity Buying Service	Y
Beltone	Sorkin Music Co	Y				kayvintagereissue.com claims distribution by “Monroe or P&H”
Biltmore	Vitak-Elsnic		Y
Broman	Broman		Y		1940s
Bruno			Y
Buckeye			Y
Carelli			Y
Catalina	Abercrombie and Fitch	Y				Not to be confused with the Harmony Catalina model archtop
Columbian	Selmer UK		Y
Commander	Aldens		Y
Continental	Continental Music Company	Y			1929-late 1940s
Coronado	Gamble-Skogmo	Y			1960s
Crest	Sears		Y		Late 1930s
Custom Kraft	St Louis Music Co	Y	Y		1930s-1968
El Rancho	Sorkin Music Co	Y			Late 1950s	Western motif
Encore			Y		1940s-1950s
Esquire	Selmer Indiana		Y	Y	1938
Fascinator			Y
Fender			Y		1970s
Fischer	Carl Fischer Catalog	Y	Y		1929-1936 1950s	Also seen branded “Carl Fischer”
Franklin	Franklin Music House	Y			1930s
Futuramic		Y			1950s	Space age motif
Gagliano		Y	Y
Galaxy		Y
Galiano		Y	Y	Y
Gaylord			Y
Gretsch		Y	Y		Wartime 1940s
Groehsl					1918-1921	Absorbed by Stromberg-Voisinet
Heath	Heathkit		Y			Primarily electric
Holiday	Aldens	Y	Y		1960s
Hollywood	Schireson Brothers	Y			1933	Commonly mispelled as “Shireson”
Jay Johnson			Y
Kamico	Kay	Y			1947-1951	Budget line of Kay instruments
Kay Kraft		Y			1927-1937	Venetian style
Kaywood		Y			1934	Wooden resonators
Lark Jr		Y	Y		1930s-1950s	Music-note inlays on the Harmony models
Lee Gibbs / Concertone	Montgomery Ward	Y	Y		1914-1930s
Liberty		Y			Post-War 1940s	Patriotic red-white-blue motif
Lombardi			Y		1930s-1940s	Also known as Nobility
Manhattan	Selmer Indiana		Y
Marathon	Southland Musical Merchandise Co	Y			1950s
Marvel	Peter Sorkin Co	Y	Y		1940s-1970s
Marveltone		Y		Y	1930s	No apparent relation to the ‘Marvel’ line
Marwin	Barth-Feinberg	Y	Possible		1940s-1950s
Master Art			Y
Mayflower	Stromberg-Voisinet	Y			1920s
McKinney				Y
Melody King	Bronson Music Co	Y	Y		Post 1931
Minerva	Eaton’s Canada		Y
Mitchel			Y
Montclair		Y	Y		1950s-1960s
Nobility			Y		1930s-1940s	Also labelled as Lombardi
Oahu	Oahu Publishing Company	Y	Y		1927-1938
Old Kraftsman	Spiegel	Y			1942
Opus			Y		1974-1975
Orpheum	Montgomery Ward	Y			1930s-1950s
Paramount	William Lange Banjo Co	Y	Y
Penn	Pennino Music Co.	Y			1950s
Penncrest	J.C. Penney	Y			1950s-1960s
Playtime	Sears	Y			1940s
Prairie Voice	Calgary Stampede		Y
Premier		Y	Y
Regal		Y	Y	Y		Kay-built in the 1930s Harmony-built post 1954
Rex	Gretsch Catalog (1948)	Y	Y		1930s-1940s
Rhapsody		Y
Royalist	RCA Victor	Y
Serenader	Buegeleisen and Jacobson	Y	Y
S. S. Maxwell		Y	Y		1930s
Sherwood	Montgomery Ward	Y			1940s-1960s
Sierra		Y
Silvertone	Sears	Y	Y	Y		Most common brand. Italian-built models exist from the 60s
Sonata			Y		1940s
S. S. Stewart	Buegeleisen and Jacobson	Y	Y		1930s-1950s
Sterling	Tonk Brothers	Y			1930s
Stromberg		Y			1921-1932
Supertone	Sears	Y	Y		1914-1941
Suprema	Eaton’s Canada	Y	Y		1930s
Supro		Y			1960s	“P.S. Supros were only built by Kay for about 2 years at the very end of their existence.” - Greg Z
Sylvia		Y
Telleno		Y
Tone King			Y
Tonk	Tonk Brothers Co				Till 1938
Tower			Y
Truetone	Western Auto	Y	Y		1950s-1960s
Vega			Y
Vibratone	St Louis Music Co	Y	Y			Resonator models exist
Vita Uke			Y			Roy Smeck endorsement
Wabash	David Wexler Company	Y
Walters			Y		1930s-1950s
Ward	Montgomery Ward	Y			1925-1961
Webster		Y	Y		1940s-1950s
Weymann			Y
Windsor	Montgomery Ward	Y	Y
Wizard			Y			References to these instruments only appear from South Africa