The MKIII target screw measures a tad over 1" measured under the head. These should work and are just over 1". Are your stocks target or service? The service stocks measure 7/8" under the head and use the Woodsman screw (listed below)
There seems to be a growing trend on the auction sites where sellers are doing one or more of the following: with holding the grip screw(s), selling single panels separately - basically I see a lot of piecing out of grips to max out the return on auction.
Granted, many times and particularly so when a weapon has seen LE use a single grip panel gets exposed and that side takes a beating. So collectors strive to find a suitable panel to match color and grain to make the grips on their gun appear "perfect" or "original" - actually period correct is the proper terminology.
Just wanted to point out this observation for anyone shopping for grips/stocks - also be sure that screw is included...