Hitachi DH 50MB Technical Data And Service Manual page 20

Drill bit
As illustrated in Fig. 12, the tool holder is designed to accept SDS max shank bits so that torque transmission
to the drill bit is accomplished with three key rails formed on the tool holder, with two needle rollers provided to
prevent the drill bit from slipping out.
The round shank, with an outer diameter of 18 mm, tends to attract less dust to itself or to the hammer drill
itself. Also, the runout of drill bit becomes less by making the guide length of the shank longer.
Key slot
Cross section A-A
Needle roller
(2 pieces)
Key slot
Key rail (3 pieces)
Fig. 12
--- 18 ---
Tool holder cross section
A
A
Retainer sleeve
Needle holder