When I build the belt loops, they are attached with the black steel or aluminum Chicago screws, using a #8 drill bit. I usually just drill the holes "by eye", and the loops is mounted that way....no room for adjustment.
The Tek-Loks are nice in that they have 9 holes in them, all spaced evenly, so that a person can place the Tek-Lok on the sheath for just about any carry position they like. Because folks will often move a Tek-Lok around until they figure out where they like it, I usually drill the holes for the Tek-Loks with a 1/4" bit, line the holes with kydex eyelets, and then mount the Tek-Lok screws through the eyelets....that way its more difficult for things to get messed up from folks taking things apart and putting them back together.