The thread in the engine block is a 1/4" NPT (National Pipe) thread. However, there is an adapter fitting that couples it to a piece of 7/16" outside diameter tubing. 7/16" tubing is extremely scarce, so it might be necessary to use 1/2" tubing and the appropriate adapters if you don't have the complete setup from the pump to the block. Going up one size on the tubing isn't a problem. It won't cause trouble with oil pressure, and the volume from the pump won't be affected.
Jerry
