IRS Swing arm pivot bolt size question

[topconker]

Need to replace the IRS swing arm pivot bolt on both sides.
Looking at Haynes it states a box spanner will undo the hex head, but what size is it?
Think I'd like to buy a proper allen key insert so want to make sure I get the right size.
Can anyone help please?

TC

[topconker]

OK no probs found it.

17mm