Totally my opinion of course, and that's based on where I grew up and the rifles I saw around that were originally equipped with grease holes. In this case, the hole's diameter is roughly the same as that of the rifle's patch and depth is approximately one half the thickness of the stock. In use, it was common to have a pre-cut patch pressed into the tallow/grease. After loading, that patch was replaced with a fresh one. The few I've added to rifles were done with a brace and bit. Kinda slow going, but cuts a clean hole and it's easy to keep things under control.