The reverse cut ring gear
has an extra
anti-deflection support,
provided by a thrust
block.

The thrust block is used
in late model and sprint
car quick change rear
ends.
THRUST BLOCK
Grade 8   3/4 inch fine thread adjuster
With the thrust block,
extra case ribbing isn't
as critical because the
case doesn't flex like a
non thrust block case;
due to the fact that the
ring gear side load is
controlled at the point
where it occurs instead
of 3 inches away at the
bearing.
The 3 pictures below show a reduced diameter ARB and Detroit Locker
to allow for the thrustblock. The heavy duty full spools are this size
already.
There will not be a thrustblock used with the
factory trac locs because of their case design.