Most are home made. Mine is, I simply ground a point on the end of a 1/2 inch bolt about 6 inches long. Added nut and washers making my base center. Attach this to the table of your drill press. Mine is sort of permanently attached to the edge of the round table. Put your chosen drill into the chuck and align it to the point of the bottom center, allowing for the thicknes of the work. Lock your table and your ready to go. For jobs like tang bolt holes, I typically will lay out and center punch,then drill a undersized pilot hole freehand. I’ll do this with the trigger plate also.Then double check for center, if it’s a bit out I’ll use a countersink and chisel to draw the countersink to center. You nick the edge of the hole in the direction you need it to go. Once centered I’ll countersink useing the center jig to nearly finish diameter. Then drill your clearance hole to the trigger plate. The drill will center itself in the countersink. Then flip the stock, change to the tap drill and drill the trigger plate. That’s my method for what it’s worth. BJH