The National C-175 is a 17½-inch bore rotary table (i.e. the opening where the drill string passes) with nominal 44-inch centers between table axis and inner row of sprocket
It's part of the “C” series of National / NOV rotary tables for drilling rigs.
From references and comparative charts:
| Parameter | Approximate / Typical Value |
|---|---|
| Bore / Opening | 17½″ (≈ 444.5 mm) |
| Center distance (table axis to inner row sprocket) | 44″ (≈ 1118 mm) |
| Static load rating / capacity | ~ 250 tons (some sources list “C-175-S 250” variant) |
| Gear / pinion ratio | (~) 3.58:1 (for the 17½″ class models in similar design) |
| Maximum speed | Rotary tables of this class typically allow up to 300 rpm (intermittent) |
| Dimensions (approx) | The overall external size for “RP175 / C-175 class” models ~ 76″ × 50″ × 23″ (L × W × H) |
| Weight | ~ 8,600 lbs (≈ 3,888 kg) for the base assembly (no extras) |
| Bearings / internals | Uses alloy steel pinion & gear sets, API master bushings & bowls, reliable seals, API 7K compliance |
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