The ones I am familiar with are not threaded. Nor are the ones in the photo.
They certainly are threaded. At least on an AD truck. The attached picture is one that had a broken bolt when I removed my strikers. They're not shims, they're nut plates. They're installed with the serrations toward the striker so they don't move once the bolts are tightened. For shimming the striker, washers can be used between the striker and the oversized holes in the latch pillar. BTW all of mine have the serrations going lengthwise as in my pic. I have never seen one with crosswise serrations.
Carl52 is absolutely correct.
