Carabiner strap mounting screw

The carabiner strap mounting screw fell out of the back of my Inreach Mini 2 leaving my carabiner securely clipped to my belt but my Inreach on the ground.  Luckily I was around camp and heard it fall, but no luck finding the screw.  Also no luck finding info on Garmin regarding screw type and size.  Would like to get a good description before I head off to the Ace to search for one.  Would hate to get the wrong size and damage the casing.

UPDATE:  Just used Chat Support function on Garmin website and as a "one-time courtesy" the representative is shipping the spline mount that Snow_Leopard suggested.  Apparently that is their solution-- no individual screws or even specs on the screw supplied. As backup for paddling I think I'll also attach a small nylon loop to the lanyard holes on the top and clip to a fishing leash.  Relatively painless as far as "lessons" go I guess since I didn't lose the device.  Whew.