Steel Diaphragm Coupling (Black Oxide)

What it is

The 45# steel series is our heavy-duty diaphragm coupling, built from black-oxide 45# carbon steel hubs and a one-piece 304 stainless steel diaphragm. It is engineered for large servo motors and spindle drives where aluminum couplings simply cannot carry the load.

With a stepped diaphragm design and outside diameters up to 190 mm, this series delivers the high torsional strength and long-term durability that production machinery demands. It is offered in single-diaphragm and double-diaphragm versions to match your stiffness and misalignment requirements.

Why engineers choose it

• Heavy-duty 45# steel hubs — far higher torsional strength than aluminum, for large drives.
• One-piece 304 stainless diaphragm — zero backlash and high stiffness with corrosion resistance.
• Large diameters — up to 190 mm OD for the biggest servo and spindle applications.
• Single or double diaphragm — choose single for stiffness, double for more misalignment compensation.
• Black-oxide finish — durable surface treatment for corrosion resistance and a clean look.

Key specifications

Full range

Data source: CROCNC internal quotation sheet. Custom bore diameters and keyways available on request.

Where it's used

• Large servo motors and spindle drives
• Heavy CNC machining centers
• Printing presses and converting machines
• Metal-forming and press equipment
• Wind and renewable-energy drivetrains

How to choose the right coupling

Choose the 45# steel series when your drive torque exceeds what an aluminum coupling can safely carry, or when you need maximum durability on a production machine. Pick the single-diaphragm version for highest stiffness, or the double-diaphragm version for more misalignment tolerance. For lighter applications, the CRO-CS aluminum diaphragm coupling is the more economical choice.

Frequently asked questions

What is the difference between single and double diaphragm?

The single-diaphragm version is stiffer and more compact, suited to well-aligned shafts. The double-diaphragm version adds a second flexing disc, allowing more angular and parallel misalignment compensation at a slightly longer length.

What torque can it handle?

The largest sizes handle up to 1,040 N·m of rated torque. Because torque needs vary by speed and duty cycle, send us your application details and we will confirm the correct model.

Is the black-oxide finish enough for outdoor use?

Black oxide offers basic corrosion resistance. For continuous outdoor or wet exposure, we recommend additional treatment or our stainless steel couplings.