Is it the 25mm oil drain plug?

Just curious.

 

I'd guess either the axle nut or the front crank nut based on other cars (not a 2/7/9). I have odd sockets like a 36mm for axle nuts on my 850.

 

The crank bolt is 24mm on my 2/7/940's.

I've never done any wheel bearings...so that axle nut may be the biggest on these cars.

 

27 mm on my '86 245 for the front hub nut. It is castellated (needs a cotter pin) but is not on very tight at all. By the way, I use a 1" on that drain plug; it fits just a bit tighter than 25mm. A number of other fasteners that escape memory right now fit SAE wrenches better than the metric on these cars. The strut cartridge nut that holds the front strut cartridges is huge, but needs either the special Volvo tool or an improvised method of removal/replacement.

 

I just recently replaced the front struts, mounts and bellows on my 740. The strut/gland nut on the passenger side strut assembly would not budge for me and my pipe wrench. I took the whole assembly into a volvo shop and they got if off for $20. The top nuts under the hood were no problem...and 24mm...which put my original question into my head.