ARB RD44 - Manual (Page 11)

2 Removing the Existing Differential
9
2.7 Use of the Thrust Block
As this Air Locker has been designed to cover a range of Isuzu
applications, some installations may require a floating thrust block
(supplied) to be inserted into the diff center. If you are unsure whether
this applies to you, look down the splines of the OE diff you have
removed from the vehicle to see if a thrust block used to maintain axle
end float is present.
c Remove the flange cap and splined side gear from the Air Locker.
c Insert the thrust block into the diff center and replace the splined
side gear and flange cap.
HINT : A wad of thick grease will help to hold the thrust block
in place during installation.