I think there could be an issue with the original statement about the difference between Ottawa and Philadelphia 1968 10 cents.
I have seen 1966 silver 10 cent with flat-bottom grooves and I have 1968 nickel 10c with flat grooves in plio-film which were all made in Ottawa.
Also, 1968 10c mintages by RCM and by Philadelphia mint are about the same, but coins with v-shaped grooves are much more common.
That indicates that both mints have used flat-bottom collars.
Maybe Phily 10 cents do have flat-bottom grooves, but it does not mean that Ottawa did not use the same type of collar.
One article was telling that Phily mint had used US dime collars, but I believe it is a mistake.
US dime collars are quite different with the number of the reeds and their shape.
I have seen 1966 silver 10 cent with flat-bottom grooves and I have 1968 nickel 10c with flat grooves in plio-film which were all made in Ottawa.
Also, 1968 10c mintages by RCM and by Philadelphia mint are about the same, but coins with v-shaped grooves are much more common.
That indicates that both mints have used flat-bottom collars.
Maybe Phily 10 cents do have flat-bottom grooves, but it does not mean that Ottawa did not use the same type of collar.
One article was telling that Phily mint had used US dime collars, but I believe it is a mistake.
US dime collars are quite different with the number of the reeds and their shape.


















