For some reason only one outfit I know of sells these for a reasonable price ($25/pr), but I've found them immensely useful on my atv over the past 4 years.
Before you go "rifle rack!" - I actually put these on for carrying my Echo srm 410u brush cutter. (I have a different idea for the gun rack )
Install is pretty straight forward, but my local hardware stores (in the sticks) didn't have the 2" u-bolts in 1/4" like the kolpin mounts. I bought 4.5" 1/4-20 bolts just in case, but did find some 5/16-18 u-bolts that looked like they'd work with the mounts if I drilled them out. So I got some nyloc nuts for the bigger bolts and headed home.
Upon test fitting the 1/4-20's, I discovered the 5/16 u-bolts actually fit the ROPS better (happy accident!) and so I proceeded to enlarge two holes in a bracket and try it on the hoop. Looking real good at that point, I drilled the remaining holes and shortened the u-bolts down to 4" from the inside of the bend using a cut-off wheel in my cordless angle grinder. After that, I swapped out the disc for a flap wheel and cleaned up the ends.
I also align-drilled my ROPS holes as well as replacing the pins with D-ring hitch pins. It's MUCH easier to work the hoop now.
Don't mind the date. I used a cheap camera we got a couole years ago and didn't set it up after recharging the battery.