Caution, in flushing and cleaning the A/C strainer this weekend, I was reattaching the hose to the nipple coming from the raw water thru hull. In simply re tightening the hose clamp the nipple sheared off. Then in trying to carefully unscrew the remnant threads that screw into the 90 elbow they completley crushed. It looks to me like the nipple is copper and quite thin (are not dissimilar metals a no no), not sure of the material you can see that was it's threads. In any event, if this had happened at any other time when I wasn't standing over it, it could pretty quickly sink your boat.
I looked at all the other thru hulls and this is the only one that is configured this way. Scary stuff. I would go look at yours right now.
West marine had the new bronze 90 3/4 NPT elbow and the corresponding BRONZE nipple. Cost apporox. 50.00 including the teflon tape.
Shocking to me that such a vital part would be such a weak link.