22 mm for an '01. I use a plumbing drain/pipe socket to remove mine. A set @ Harbor Freight costs $10, and you get 10 different sizes. Works like a charm.

 

my dude! ^

 

09 zx6r? i use a 13/16 spark plug socket it u use the oposite side it fits perfect. im a mechanic and luckily had 2

 

That's equal to a tad over 21 mm, but less than 22 mm. It'll work too.

 

yeah it fit mine perfectly.

 

Made mine from an old bit of hex rock drill and a socket welded together. Carry another in the extra tools bag just in case of a flat.

gammac

 

Tack welded a nut and bolt together to make the one we use.