Even the emergency service is pretty stunned for a 2CV if the contact no longer does what it needs to or the V-string hangs in the fan housing. The 14 mm cap with 1/2' drive is sometimes too thick and does not fit in the propeller.

Many 2CV drivers therefore have a 14 mm pipe key with them in their on-board tools. However, for permanent use, the key available in regular stores is quite stupid. These things have holes to insert a screwdriver or something like that and act as a lever, but how often has a screwdriver broken off if the bolt is too tight? The remedy is a normal cap key size 18, which fits perfectly on a standard 14x15 pipe wrench on the 15 mm side. So you can unscrew the bolt safely and easily with a 1/2' drive or ratchet. Also looks great this tool...

You can also use a 19 mm ring wrench and the mentioned water pump pliers. Another option is to use a perfectly normal 14 mm cap with a 3/8' drive and extension, which is thin enough and fits depending on the manufacturer. I myself use a long cap from Facom with a 1/2" connection. This also makes the fan a bit wobbly and possibly loosening a little left and right. One never stops learning...