[one bullet]

That's one of the reasons I was puzzled. I had no idea at first what brand it was so I did a generic search. Some of the Gen4 plugs clearly had the little nub like the Gen3's and I noticed mine had been cut off. I had no idea that it took a screw until I figured out what brand it was.

 

[one bullet]

Sounds like you have a Jentra brand plug. When Gen 4's came out I think they beat eveybody to the market with the grip plug. It would only work without the backstraps in place and had the little screw. I remember putting one in my department issued model 31. May be wrong on the date but maybe 2011 or so.