ID on an Omega Speedmaster Bracelet

I am trying to ID a peedmaster Bracelet I have had for a long time. It is marked on the inside blade of the clasp No. 12 in an oval outline (with the Omega logo and Stainless Steel, and also 2-71 on one end of one of the blades. The Endpieces are 19mm and are only marked 77. Trying to find out what model it is. Looks like it was made in Second quarter 1971, I think. Any help would be appreciated!