Bob Freitas asked about this 1930s ( or posibly earlier) double chainring, as to how it fitted on to the crank. I haven,t been able to foind the item on Ebay but assume it is similar to another one - different number that is currently for sale , and has attracted aone bid so far.
I think that the bidder might be assuming that the chainring has the standard 5 small holes, on the style of TA and Stronglight. Howver these early ROSA/ Cyclo models were quite different in having a fine thread cut into the circular hole that fits on to the crank. In its turn the crank has a boss forged onot its back, the boss being turned and threaded to accept the chainring. I assume that the thread is standard R?H so that the ring tightens under the pedalling force.
This type of fitting was quite common in the 20/30s period being standard on cycles such as the Alcyon. Recently I bought two such bikes in France - an Alcyon ( a 1920s ex Tour de France machine) and an AQUILON. The chainrings are identical, both internally threaded and both bearing large letter A s within the design of the chain ring. The rings are in good fettle, but I am still struggling to remove them from the cranks, so that I can have the latter rechromed.
The cranks are a bit of a rarity to find, so I hope the bidder for the double ring on Ebay knows what he or she is buying.
Norris Lockley... looking for a sprocket removing tool with about 15" of chain attached.