I've been restoring a Seth Thomas street clock, and part of the project is to have several missing pieces cast at a local foundry. I picked the new pieces up a couple of weeks ago, including this weight, and today we drilled and tapped the 5/8"-11 hole for the original brass pulley. I bought a new 17/32" drill bit (I always buy Cleveland bits) and let's just say it wasn't cheap! After drilling a pilot hole and enlarging it, we used the new bit to finish it off, being very careful to maintain plumbitude in both directions. We then used a taper tap to thread the hole, followed by a plug tap and a bottom tap. The pulley threaded in easily, as it should. I decided to have the weight and the base doors (the other parts I mentioned) cast in ductile iron- mostly because the doors will be stronger than cast iron, and this clock is going to a new home in a public park, on a very busy street in a very busy downtown area. The hole in the weight proved very easy to drill and tap.