Graham
You should be measuring the cutting edge length not from base to tip. By my maths 8.58 base to tip translates to 9.9 mm cutting edge length. Allowing for tip radius that would be 10 mm cutting edge length. So the ISO standard number insert would be TCMT 10 02 08. Which doesn't exist! Nearest ISO sizes are 9 mm and 11 mm cutting edge length. You have a non ISO standard tip and holder set so you have to go back to the orignal supplier.
ISO tips and holders of the same nominal size are essentially interchageable between makes.
ISO standard holders should have a type number on the shank of the holder(s). If so it can be decoded to identify the tips its supposed to take. Its usually easier to work back from the holder number to tip size than to try and measure the tip itself. Especially if you haven't got a decent chart showing what the tip numbers mean and exactly where to take measurements. I found a good one from the Iscar catalogue, not got the link tho'.
Clive