Summary

for https://www.etsy.com/listing/738337544/celty-sturlusons-scythe-from-durarara

Each blade is different. You may have to tweak the "blade" object for everything to fit right.
Make a test print of the support, and test fit it until it's perfect, before drilling ANY holes. If you mess up, you can always move the screwclear objects around to compensate.

I printed mine in black PETG, with light sanding.

The drillguide should fit over the blade, support, and PVC. The hole in the top is to allow you to verify that everything is lined up properly. Use a drill bit that just barely doesn't fit into the holes of the drillguide.

I use m4 screws, and m4 "7mm wide 12mm long" hex coupler nuts. https://www.amazon.com/gp/product/B0CLLC78S8 and https://www.amazon.com/gp/product/B08YM9RPP2

8-32 screws should also work, if you don't use the coupler nuts.

If you're going to use these coupler nuts, you should drill out the blade's holes with a 5/16th's bit and press-fit the coupler nuts, using the support for alignment. Once they are in, you won't be able to remove the support. You can use a screw to "pull" the nuts into place.

Otherwise, if you just want to run a bolt all the way through and avoid the coupler nuts entirely, just use the "screwclear" versions. These also allow a bit of room if your drilling isn't super precise.

Everything is clearanced so that its a tight press fit, and the screws will need to be "threaded" into the plastic support.