There are a couple different types for the MK1 depending on production date.Sometime in the early seventies,I believe,they switched the mags from having the follower button on the right side of the mag to the left side.If your button is on the left side it's a later production and MK2 mags will fit.If it's on the right it's early production.You can make MK2 mags work in the early guns by switching the follower button to the opposite side.I ordered mags for my MK1 from 4 different places before someone actually shipped them to me.