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Does anyone have the BSA part numbers for the 1956 rigid frame flat track bike rear bolt on sprocket and hub? Does someone have both items to sale. I have a bolt on rear hub, but not sure it is correct. It has10 pcs 5/16 bolts on a 7-5/16 register and 8-5/16 bolt center.

Okay, It sure is quiet out there! Maybe a little more information will help. The sprocket hub that came with the bike when I bought it has a 7.312" register and 10 5/16" bolts on an 8.125 " bolt circle for 1/4" chain. I am looking for approximately 50 teeth.

The A65/B44 crinkle hub sprocket/brake drum with the bolt on sprocket fits the earlier single and twins crinkle hub.
The standard sprocket is 47 tooth and is available in 530 size or 520n size. I have one of these on my Goldie rep which allows me to use a 520 O ring chain

20220422_091547 by Sigma Projects, on Flickr

Do you have Goldstar or A65 brakedrum?
The original Flattrack GS is not made for using brake shield. The A65 is.

The rear sprockets have different par no depending on amount of teeth so it would be hard to find as it was only for these few racers.

The BB32R framed flattrack racer used the narrow chain 520 but you can use the easier to find sprocket for 530 chain.
You can use a 1965-66 A65 rear brakedrum it fits well I have that on my street legal racer that has brakes.
The 1956 Goldie "brakedrum" was bare and not used for brakes. I have one of those genuine that goes on when racing.
BSA supplied the bike with three rear sprockets 50-51-52T the gearboxsprocket was 16T from factory and narrow 520.
Have no partnumbers but check if B44/A65 rear works for you.

I believe Donelsons in Saint Louis has the sprockets

see this image, left is original 1956 flattrack never mind that the drum has extra wholes drilled or the sprocket is painted
The right is A65 1966 and I used a sprocket for 520 sprocket instead of the A65 530 widht.
Narrow 520 width ⅝" x ¼"
530 width is ⅝" x ⅜"

Oh the left cant take a brake shield with those bolt heads but the A65 1966 can..
if you use A65 parts then you can use the original bolt heads they have harder steel than the allen

Oh I dug deep and found this picture
see Sprockets for Gold Star
50 tooth 67-6201
51 tooth 67-6205
52 tooth 67-6206

The drum is also named as
67-6168

Thanks to everyone for the detective work. I have found a complete original NOS hub complete with the three sprocket. Thanks Dan! Lloyd L

Wow that is fantastic. I would love to see photo of the hub and sprockets

As soon as it comes in the mail I will post the photos.

Well, the rear hub has arrived at my shop. I would like to thank Brit Twit for giving these parts a home until I needed them. He brought them from Gold Star Freddie several years ago, NOS parts. The set came with the hub and three sprockets, 50,51, and 52 teeth. I am attaching a photo of the hub and some measurements to identify them in the future.
The sprocket is held in the correct position on the outside diameter of the hub and the counter bore of the sprocket.
Please note, I corrected the sprocket ID counter bore.

Hub outside diameter- 8.615"
Raised boss diameter-7.310"
Bolt Circle 8.025" with 10 (5/16" CEI hardened screws)
Sprocket inside diameter- 7.375"
Sprocket register counter bore inside diameter 8.620” (0.090" deep)

Fantastic, I got my original hub as well from Fred but it had the six drilled holes in order to make it lighter. see my previous post with black hub and sprocket.
Thanks for measuring the parts. Since I was making my bike for road use I could not use the racing hub as the brakeplate did not fit with the bolts.
Instead I used a 1965-66 A65 hub which is slightly different.

Thanks for the post!

As a possibly interesting aside, the 1961 announcement for the Special Competition model said it came with "bolt on sprocket with extra sprockets of 51 and 52 teeth being supplied with machine," but a subsequent bulletin corrected that and said it only came with the 50-tooth sprocket, with the others available as extra-cost accessories.

Magnetoman
1961 Competition models had S/A frames.
1956-58 was the years for the factory BB32R rigid framed Gold Star Dirt Tracker and during those years bikes was supplied as stated with brakeless hubs including three 50-52T sprockets.
It was of course also sold as parts supplied by the US importers/dealers so you could use it for any BSA that you wanted to race.
Hopefully these copies are good to read

Right. I included that aside because I thought it was interesting that BSA still considered 50, 51, and 52 to be the most appropriate sizes for tuning the overall gearing on the later Gold Star as well.

Do you know what gearbox sprocket they used on the comp model in 1961?
The flattrack model had 16T from factory.

The 1963 West Coast list shows 21T engine, 50T chainwheel (with 51T and 52T as "spares"), and 19T gearbox.

The two big competition sports in Britain and Ireland at that time were Trials and Scrambles. Riders often used the same bike for both, lowering the gearing using interchangeable sprockets.