what size thread are the Shift knobs
 

and will these shift knobs fit:

Classic T-Handle Knobs
Smooth and comfortable are the name of the game with these T-Handles. Choose either the brushed or chrome finish, both have the embossed B&M logo. Handles with the button make it easy to activate any line lock, transbrake or nitrous system without having to remove your hand from the shifter. Works with 12 or 16-volt systems. Includes thread inserts to fit 1/2'' - 20, 3/8'' - 24, 3/8'' - 16 and 5/16'' - 18 thread shifters.

Hammer Head T-Handle Knobs
The same ergonomically designed handle featured on the Hammer shifters. Fits your hand comfortably and features an Chrome plated aluminum finish. 130-80741 includes adapters to fit 1/2'' - 20, 3/8'' - 24, 3/8'' - 16 & 5/16'' - 18 thread shifters; 130-80742 fits 1983-96 Camaro/Trans-Am 16mm x 1.50 threads and 1983-96 Mustang 12mm x 1.75 threads.

I believe they are 10mm x 1.25mm thread pitch (at least that was the Miata size, and my Miata knobs fit my RX8 just fine).

s0 are these going to fit it?

You do know that ALL the T-handle shift knobs that B & M makes are designed for AT?
Not one T-Handle in the MT shift knob section.
http://www.bmracing.com/products/acc_manual.html
To answer your question I don’t think the Hammer Head will fit. They do carry other T-handle’s in Metric the 80550 & 80551
http://www.bmracing.com/products/acc_auto/tHandle.html
but again you are planning to use an automotive part for something it was not designed for. Good luck, rigging things can be fun but I wouldn’t do it with something as important as the gear shifter.

That is the thread size listed by Team Voodoo as being for both the Miata and RX8.