We had a "Shop Gun" Ruger MKIV that I screwed up trying to fit with an aftermarket sear. The factory safety had to be modified to fit that sear. Later we were testing other aftermarket parts and afterward, the safety didn't work anymore... It would not engage the sear. Ruger factory wouldn't sell a replacement safety. I had some big ideas about adding metal to fix the safety but procrastinated on that. Then I saw that Tandem Kross had just introduced this new TK safety for the MKIV. I ordered one right away. At first, installation looked like I'd have to do some fitting. Then I realized the gun had more problems than just the safety... It had some experimental parts inside including the sear. So I decided to fix everything with a Volquartsen kit... To replace pretty much everything. This went together with the TK safety with zero fitting... This safety was a drop-in fit with the Volquartsen sear and the rest of the kit. And now, our "Shop" Ruger MKIV works perfectly again... Thanks to the Tandem Kross MKIV Safety. I'd give it 6 stars but there's only room for 5.