4Crawler recommends sleeved bolts through the frame if you want increased strength while still keeping the sliders removable.



(from 4Crawler website) Choose a bolt location where the back side of the frame is clear of brackets and obstructions and simply drill a 3/8" hole clear through the frame and install a bolt about 1/2" longer than the frame is thick and back up the nut with a large, thick washer. If the hole is relatively close to the bottom the the frame, there is no need to sleeve the bolt hole. If a sleeve is desired, a length of 1/4" - 3/8" schedule 40 water pipe, cut the fit inside the frame will work great. An 9/16" - 11/16" hole needs to be drilled in the outside face of the frame then it should be tack welded in place to keep it in place, or using the pre-tapped mounting brackets, thread the end of the sleeve into the bracket then slide the sleeves into the holes and secure with a combination of self-tapping bolts on top and sleeved bolts on the bottom.

When drilling through the frame and when tightening the thru-bolts, be extra careful to not drill into anything behind the frame, such as brake lines, wiring or the gas tank. If a thru-bolt seems like it'll stick out too far from a nut on the inside of the frame rail, it is perfectly OK to cut the threaded end shorter or install a few extra washers under the head of the bolt to shorten the rear projection.