I have two tri lug guns, a B&T APC9 Pro and a H&K SP5. The SP5 specs are slightly different on the tri lug, with it being wider at the rear of the lugs by about 0.02". This mount won't work on the SP5 without modifying the SP5's lugs.
I spoke with HUXWRX and they confirmed as much.
RAD 3-Lug Adapter5
Posted by mark plattner on Mar 28th 2022
Easy to install and best of all it worked on various tri lug barrels , even those with 1/2x28 thread covers on the tri lug