Depending on what engine you have, they may be screw in or freeze plug type.
I have my 8L big block Chevy on an engine stand about to put freeze plug heaters in.
If I can make the pictures small enough on my phone to post on here I will.
Look for a post soon for an immersion oil sump heater using a 1,200 watt hot water heater element.
1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.