DD, Pig is pretty much onto it. There is no synchromesh mechanism, this is replaced with a 'Dog Only' setup that is rough, but very fast. A bit of a 'smash and grab' operation. THe dog also has a slight ramp on the dog engagement face, usually between 2 and 7 degrees so under load the selector ring and dog ring pull together. Synchro's generally get worked too hard and brass burns out very quick in motorsport applications.

I'm suprised that nobody has mentioned that 1st gear has 6 dogs while the rest have 8 dogs. All our early stuff has 8 dogs. The early GRA-5 (group A) and GRA-N6 (Group A Nissan 6 speed) as well as the H6S were 8 dog but later were revised to 6 dog with pretty much all the sequential box's as it offers a larger window to select gears and offers no less structural integrity to the gear itself.