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The master bushing (Fig. 10.2) is a split steel casting with
API standard driving square for the kelly bushing and slip seat.
Recesses are provided in the bushing for a lifting hook to facilitate
handling on the rig floor. The bushing is seated in the table casting.
Early tables had, in place of the square for the kelly bushing, a grip
ring attached to the turntable. The rollers clamped directly on the
drill pipe. This drive often resulted in crushed drill pipe.

Figure 10.2 – Master bushing

A natural modification was the introduction of a heavier-
than-drill-pipe griefstem to ride in the grip ring. The familiar kelly
soon followed. Much later a table ring guard, with a non-skid tread
on its upper surface, was introduced to provide greater safety for
the men working around the rotary. It also provided a convenient
place to set the slips on trips.
The pinion shaft assembly consists of an alloy steel shaft
with the pinion gear shrunk on it. The shaft is supported by two
roller bearings mounted near the respective ends. Shaft lock collars
are mounted on the shaft between the bearings. Two pawls
manually actuated by handles mounted on the outside of the table

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