A plunger to fix the broken one on SECO surveying rod holders. The stock holder is either metal (doesn't break) or a poor quality plastic that does break. This is for a nylon print that should last a lot longer than stock. The screw hold is printed at the drill diameter for the tap for a 4-40 thread. All you should need to do is tap it. Normally I would suggest a Helicoil insert, but, there isn't a lot of material outside of this hole and once set it really doesn't need to come out again.