I don't remember that part having a number by itself. I think it was part of the LU60A Incandescent Lamp Module which also included the bezel and P60 lamp assembly. That's definitely an old one you have there.
If you're looking for a replacement that doesn't have the hex, you could try the one from OVEREADY. However, it doesn't have the knurling either. You can see some pics of it in use here.
That particular adapter can be found if you take your time but it will probably come along with parts you may not need. Hint. Look for the earlier (metal bodied) SF pistol lights like the P116 or similar. That's how I got mine. Took me awhile to figure out the one in the photo can be found. Just be patient.
Great info, thanks...I looked up a few weaponlight assemblies and it does look like they are going to be few and far between...and come with extraneous parts surplus to requirements.
Great information however...thanks for taking time to post.