Hitachi DH 50MB Technical Data And Service Manual page 21

Tool holder
The tool holder is described below with reference to Fig. 13. The drill bit inlet is covered with a front cap
(rubber) to prevent entry of cutting chips. Two needle rollers fit into the round groove of the drill bit to prevent it
from slipping out of the tool holder, while the three key rails provide positive torque transmission to the drill bit.
The drill bit can be easily removed simply be pulling back the grip. The grip is spring-loaded in the forward
direction so that pulling the grip fully backward allows the needle rollers to move away from the bit. When, on
the other hand, the drill bit is pushed fully until it stops, rotating it by hand, the latter spring back to bring the
drill bit to a locked position.
When removing the drill bit, pull the grip fully backward and pull the drill bit out.
Forward
direction
Front cap
Backward
direction
Needle roller (2 pieces)
Retainer sleeve
Needle holder
Grip
Fig. 13
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Spring
Key rail (3 pieces)