I've been building old bikes for about 50 years now. I love these old style terminal boxes to keep my wiring neat and easy to get to. Makes diagnosing electrical problems, (should you have one) a breeze.
This was exactly what I needed to add a rear block for a turn signal circuit to my 1940 flathead. I ended up using the metal lid separately, making another electrical block out of it for the front of the bike.