I was removing the cylinder head on my 91 integra and a very brittle sensor broke. I don't know which sensor it is, but view this picture to see an arrow pointing to it:

http://home.comcast.net/~maxoctane/11_1_b.JPG

Anyway, even after it broke, I could not get it to unscrew. It was in there pretty good. All of the used cylinder heads I see on ebay have that sensor still bolted into the head as if it doesn't come out. Anyway, if I need to replace the sensor, do you know which sensor this is? I'm assuming it's oil pressure, or water temerature but I really don't know. Thanks in advance.