Need opinion 51/55 P bass ferrules

Sure those look fine. I've made them to almost exactly those dimensions. Brass is fine; you could even make them from aluminum if you like.

 

@Bruce Johnson - I'm considering a build with ferrules like this on both front and back side, but my big question is this: Will the "hole" in the middle cause any sort of chaffing on the string and eventual breakage? Or will it be fine? I'm less worried about the edge of the top ring and more worried about the edges down inside.

 

Hey TerribleTim;

If you are putting a "guide" bushing on the front side of the body, it should have a good radius on the edges of the hole that the string leans on. Don't bend the string over a sharp edge. Also, use a softer metal for that bushing, like brass or aluminum, not steel or stainless.

 

If the strings rest against the holes in the bridge plate then, no, you don't need an additional bushing underneath bridge. If the bridge is mounted forward of the through holes, then it's a good idea to put metal bushings in the top surface of the body so that the strings aren't bending over an edge of wood.