Walter - Before you go replacing parts you should figure out where it is coming loose to change the point gap, if in fact that's what is causing your issue. One thing that occurs on new points especially is the rubbing block (the part that rubs on the cam) wears rapidly, which causes the point gap to close. The solution to that is to polish the cam so that it gleams, and to lightly lube the cam with some grease (I use SuperLube 92003 with Teflon, but there are many other perfectly acceptable ones out there). I had one set of points wear from 0.022" opening to less than 0.016" in less than 500 miles before I figured that out. BTW, newer replacement points seem to have less of an issue with that than ones made say 5-10 years ago.
The point block (assuming you have "original" style points with a separate block) have a screw that compresses the block around the adjustment screw to prevent it moving. If that compression screw is loose, missing or stripped you will not have any way of holding the points in adjustment. Photo below shows a point block, the compression screw I'm talking about is the one on the top.