This handy device makes laying out lug mounting holes a breeze. There are two rectangular "viewing ports" that can be used to perfectly align the jig with your lug centerlines. There are three marking holes: the outer holes are for the lug mounting screws, the center hole is your drum's horizontal centerline (you probably won't need to mark this on the drum).

I included the .stl file ONLY to provide a visual representation on here. You MUST customize the .f3d file to fit your drum as follows:

1. Measure your lug mounting hole spacing, from center to center, in millimeters.
2. Open the .f3d file in Fusion and edit Sketch 8 so that the center hole is half the depth of your drum (69.5mm in the screenshot), AND the marking holes are half the mounting hole spacing from the center (24mm in the screenshot).
3. Edit the very first Extrusion (second step in timeline) to be 8 mm less than your drum depth. This will take the thickness of the "T" part of the jig into account.
4. There is no need to edit the location of the top "viewing port", as it is constrained from the end of the extrude.
5. I printed mine with PLA, 5% infill, 2 walls, and no support. It is absolutely essential that you prevent the base from warping off the build plate while printing; I used an 8mm brim for that.

Drilling tips:

1. For maximum accuracy, mark the holes with a thin scratch awl, or a small nail or drywall screw, not a pencil.
2. Use a brad point drill bit of the appropriate size for your lug mounting screws. Brad point bits tend to create tearout on BOTH sides of the hole; see next step to prevent this.
3. To prevent tearout on the OUTSIDE of the shell, run your drill in REVERSE for a second or two, with some downward pressure. Then switch to forward to finish the hole.
4. Use some type of backer board on the inside of the shell to prevent tearout there.

Enjoy!