Figure out where you want the lug, or pick two spots for two lugs. Drill from the bottom using a drill smaller than the diameter of the threaded part of the lug. Then select a Forstner bit the same diameter as a SS T nut. Using the existing small hold to center the bit, drill from the top with the Forstner bit to create a recessed flat just deep enough to accommodate the T nut. You can also do this job with a spade bit, but be sure it's nice and sharp. Drill from the top and enlarge the hole just enough to accommodate the shank of the T nut. Drill only deep enough to accept the T nut, not all the way through. Then enlarge the remainder of the hole with a smaller bit just large enough to accommodate the threaded shank of the lug. If you want to get fancy, you could take a small Forstner bit and make a small recess on the bottom of the forearm for a washer, but I didn't. Then put a bit of epoxy on the T nut and tighten it using a suitable screw and washer to protect the forearm, tapping it into place if necessary, depending on if your T nut has little "teeth" or holes. When the epoxy is cured, install the lug, trim it to length if necessary, and try your tripod.