There are several ways you could install exhaust tips, including drilling and tapping or pop riveting them, but here is a nice easy way to install them with just a couple basic tools and hardware. Stainless hardware used in this how-to is included with Lowbrow Customs exhaust tips (available for both 1.5" outside diameter and 1.75" outside diameter exhaust pipes in a variety of styles), and includes a pair of 316 stainless steel 10-32 x 3/8" button head allen bolts and a pair of 316 stainless steel nylock nuts.
The particular pipes in this article were made using the Biltwell Builder Exhaust Pipe Kit, which features 1.75" OD (outside diameter) tubing and assorted HD exhaust flanges. The Shovelhead exhaust flanges included in the kit were used on this set set of custom pipes towards the ends as convenient mounting tabs.
The flange on the exhaust tips shown is .6", a mark is made .25" from the edge of the exhaust pipe. Make sure to drill your mounting hole the bottom or inside edge of the pipe so that when they are mounted the hardware will be hidden.
To make sure your drill bit doesn't wander, center punch your measured mark.
Drill through the exhaust pipe first, then either clamp or firmly hold the exhaust tip in place and drill through it as well. Make sure the tip is thoroughly seated in the pipe before you drill it.
This will give you a perfectly lined up mounting hole. A rat tail file helps debur the drilled holes.
The nylock nuts provided with the Lowbrow Customs exhaust tips are rated at 250+ degrees F, but a dab of locktite is never a bad idea to make sure the nut doesn't ever back off from vibration. Insert your hardware, and using a 3/8" wrench and an allen, tighten it down, and you are finished.