This thermostat is like nothing I have seen. Rather than drilling your own 1/8" hole to allow for steam venting, it has what they call a jiggle pin valve. It's a 1/8" hole with a little cover over it that opens when any pressure is present.

http://www.rockauto.com/en/moreinfo.php?pk=100490&cc=1442228&jsn=416


Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet