These bullet guides are for the 5.45x39 Saiga and Vepr rifles. Installation of this guide allows your rifle to feed high capacity AK74 magazines. Shown below is a guide install kit shown with #8-32 drill & tap. (note: pic may not reflect actual geometry)
Flat Trunnion Kit
Mags used for testing (l to r) Bakelite 45, Plastic 45, Bakelite 30, Plastic Tantal 30, Plastic Bulg 30, Steel 30.
Round Trunnion Left, Flat Trunnion Right
The front trunnion is the block of steel riveted in the front of the receiver that the barrel is pressed into. The shape description comes from the shape of the area immediately below the chamber face.
Trunnion with Rivet Hole drilled (round or flat)
If you have a rivet hole drilled in your trunnion, select the rivet guide kit (545RTGR or 545FTGR) which includes a screw and a nut.
The bullet guides have a machined barrel relief on the front which tucks under the barrel face. The holes goes bottom dead center in the 6 o'clock position.