This is a customizable clip so you can attach a flashlight to your hardhat, if it is equipped with accessory slots. Instant Headlamp!  I couldn't find a headlamp that I liked for use with my hardhat at work. The straps that come with most headlamps are ill suited for hard hat use, and most aren't that bright and use AAA batteries. I decided that my lithium 14500 powered Sipik clone was a better light than most head lamps, and thus I decided to attach it to my hardhat.  The included STL fits a Sipik SK-68 clone onto a MSA V-Gard hardhat.  Measure your flashlight diameter and width of your hardhat slot and either edit the scad file or use customizer.  Do a test print (I used ABS with 100% infill) and see how it fits in your hardhat. You can adjust several parameters to improve fit:  Thickness: defines how thick the clip will print; thicker will be stronger, thinner will be more flexible and will help in insertion and removal of your flashlight. I used 2mm.  Release Tab Length: This sets how big the two insertion wings are. Bigger tabs will help you release your flashlight. 4mm works ok for me.  Locking Clip Angle: Controls how "bent" the locking tab is. More bend = tighter/snappier fit.  Locking Clip Reach: This controls how deep into the slot the barb will sit. If the barb isn't quite able to snap into place, increase this value. Likewise, if it looks like you have too much length after insertion, reduce this value. You want the clip to just snap in place when fully seated.  Locking Clip Barb Size: This sets how big the barb is. Bigger barb=more secure fit. Smaller barb=easier to remove clip from hard hat. 2mm for me results in a snug fit, but removal requires two hands and some effort.