6mm Titanium - Nylon flanged nuts.
$2.50 AUD
6mm x 1.0 Nylon nuts with a full flange.
TC4 - GR5
(NB; Check your racing organization if these are legal to use).
**** If you haven't used Titanium/Nylon before, the nylon part is the weakest part of the whole unit. Possibly put something like Never-Seize or similar on the bolt to ease through the nylon. They can pop out, tighten slowly.