There are also copper versions made as emergency plugs - slightly different concept for expansion than the rubber ones, but were available in various sizes at the local autoparts place.

I have been told they are more likely to last than the rubber plugs.

I had one pop from a boat engine last year and was able to get to it only by feel - still managed to reinsert the original (it was undamaged - I had just done a poor job of winterproofing, leaving some water in the block) - used the end of 22 oz hammer (detached from the shaft) and beat in place by feel only ... bloody job, but it worked.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg