What does 100CD mean on a worm gearbox?

It designates a worm unit whose worm-to-wheel centre distance is in the 100 mm class. On Anand Gears cast iron worms, CD is the primary size label across the 50–305CD range.

Can I replace a 100CD unit with a larger CD if torque is higher?

Not as a drop-in. A larger CD usually means a larger housing and different mounting and shaft positions. For more torque at the same foundation, discuss a matched special or a different family — do not assume CD is free to change.

How do I measure centre distance?

Measure the perpendicular distance between the worm shaft axis and the wheel shaft axis in millimetres — with the unit open if needed, or by careful calculation from housing faces and shaft diameters.

Engineering July 26, 2026 • 6 min read

Gearbox Centre Distance Explained (Worm CD)

Why CD is the size name on cast iron worm reducers, how to measure it in millimetres, and why a drop-in replacement must match it.

On industrial worm gearboxes, centre distance (CD) is not a minor detail — it is often the primary size designation. Anand Gears cast iron worm range is organised as 50–305CD (see worm gearboxes), with ratios typically 5:1–100:1 across the line. Understanding CD keeps replacement quotes honest and prevents “almost the same box” mistakes on the foundation.

What CD means

Centre distance is the perpendicular distance between the worm axis and the worm-wheel axis. Because worm and wheel axes are at 90°, that distance fixes how large the mesh envelope is and, with tooth design, how much torque the size class can sensibly carry. A larger CD usually means a larger housing, larger wheel, and higher torque capacity — not a free upgrade you can drop into a smaller footprint.

Why CD is the size designation

Catalogue families (NU, Adaptable, and similar industrial worms) label bodies by CD in millimetres: 72CD, 100CD, 150CD, and so on within the published 50–305CD span.
Ratio, mounting (foot/flange), and orientation (Under Driven / Over Driven / Top-Bottom) are selected within a CD size.
Aluminium NMRV-style units often use a different size code (e.g. 025–150 on the Anand Gears aluminium line) — still geometry-driven, but not always spoken as “CD.”

How to measure CD

Identify the worm shaft and the output (wheel) shaft.
Find the centre of each shaft (use diameter/2 from a known face if needed).
Measure the perpendicular distance between those two axes in mm.
If the unit is closed, measure carefully from housing features that locate the bearing bores, or open the unit under lock-out for a direct measurement.

Record CD to the millimetre your tools allow; do not convert from inches. For a full RFQ checklist, use how to measure a gearbox for replacement.

Why replacement must match CD

Changing CD changes:

Housing envelope and mounting hole positions relative to shaft axes.
Coupling centre heights and belt alignments.
The gear set that can live inside the box — you cannot shoehorn a larger mesh into a smaller CD housing.

A true drop-in replacement keeps CD, shaft positions, and mounting footprint so the foundation and process couplings stay put. If you need more capacity, discuss upsizing deliberately — new mounting, new shafts — not a silent CD change.

CD vs ratio vs power

CD sets the size class. Ratio sets speed reduction (and influences self-locking behaviour on high-ratio worms). Power and torque ratings depend on both, plus duty and thermal limits. When the nameplate is gone, measure CD first, then ratio (turn count or teeth), then shaft ends — in that order of layout importance.

Talk to Anand Gears

Send CD, ratio, mounting, shaft ends in mm, and a photo. We manufacture cast iron worm (50–305CD), NMRV aluminium, and drop-in specials from Bhayander East, Thane.

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