If you are using a new plug socket, you may just need to push down a little harder to get the top of the plug into the rubber boot in the socket. If that isn't it, I'd say to double check the size. 5/8 sounds a little small.

 

Snap on socket

You need a thin wall socket, i got mine from a Snap-On truck.

Size - 18mm

Part # s9711ka

http://buy1.snapon.com/catalog/item.asp?store=snapon-store&item_ID=2140&group_ID=1344

- Adam


p.s. we need a forum just for the zx600 (pre - zx6r - 636) bikes

 

Take the socket to the grinder. I did! Then use a magnet to gat the plug out. Use a 3/8 piece of hose to install the plug with anti-seize on the threads.
Screw Snap-on! Go to Walmart 1/4 the price for the same damn socket.

 

It does get a little confusing when people don't say what bike they are asking about and they don't have it listed in the "I ride:" in their profile.

 

Thanks everyone. I got that 18mm and it works.

 

Glad to help

 

Metric sockets and wrenches always work better on metric nuts/bolts/plugs.:rolleyes