threaded hole in D2 block

Put some coolant in my 37 D2 this morning. (Drained two years ago while in storage) and fluid began to pour out of what appears to be a 3/8 size hole. The hole is threaded as though something is supposed to be there. The hole is on the Drivers side just forward of the forward most freeze plug. Anyone know what this is for? I must have removed something and cant remember what, because it wasnt leaking last time I ran the motor...
thanks

Sounds like the block drain for coolant. Should probably be a plug in that hole or a drain faucet. The threads should be pipe thread.