Mike,,,,,,,,,,,,The Johnson Peep sights I got , were in the Muzzleloader Builder Supply websight. My catalog for MLBS is an old #18 , and not sure they have a print book any more. The Johnson sight takes standard screw in aperatures , listed on the same page. Also , as constructed , the sight is made to be mounted on top of the barrel . ...........Note , the sight must be cut on an angle to mate up with the angle of the breech plug tang. I've cut and mounted a couple w/ good success , using a single number 4 -- 40 tpi machine screw from the under side of the tang , into the under side of the sight. It's relatively easy to do , and performs the miracle of allowing you to see target , front sight , and rear sight peep. I couldn't shoot w/out it. ....oldwood