5C collets

What 5C identifies

Exactly 25.00 mm round stock is 0.400 mm (0.01575 in) below a 1-inch 5C bore. That gap is about 3.15 times Royal's 0.005-inch size window for conventional spring-collet chucks. Closer access is separate: Haas's HA5C/T5C HMDT has a 1.10-inch passage, while its AC-25 has no through-hole. Royal Products, CNC Collet Chucks, undated technical page, Haas HMDT, AC-25.

A pullback chuck draws the collet into its seat. A dead-length design can hold the collet stationary while the tapered sleeve advances, changing how the stock is located axially. The closer actuates the chuck.

Interface dimensions and capacity

The following values describe Hardinge's conventional 5C offering, not every accessory bearing a 5C label:

Hardinge, Spindle Tooling for Manual & CNC Lathes, catalog 2348J, printed page 4. The retrieved edition's issue date is unverified.

The external draw thread and internal stop thread serve different interfaces. Neither number is the workpiece bore size. Thread pitch, handedness, mating seat and available draw travel remain distinct aspects of fit; a similar-looking taper or a matching nominal bore does not establish assembly compatibility.

Manufacturer drawings also differ in their stated dimensions. Southwick & Meister lists its 5-C with 1.2495-inch body diameter, 3.393-inch length and a 1.238-20 external thread. That is product-specific data, not a replacement for the Hardinge drawing above. Southwick & Meister, Conventional Lathe Collets, undated page.

Nominal bore is not a wide gripping range

Royal states that workpieces in its traditional spring-collet chucks must be within 0.005 inch of nominal size to avoid heel or toe contact. Its separate Quick-Grip system provides parallel gripping and a larger range; those capabilities do not apply to conventional 5C spring collets. Royal, spring-collet and Quick-Grip comparison.

Heel or toe contact describes preferential contact near one end. Royal's figure is product guidance, not a universal 5C tolerance.

A through-hole is another independent limit. Haas lists a 1.10-inch (27.9 mm) passage for its HMDT manual closer, while its AC-25 has no through-hole. Both are offered for the HA5C/T5C family. A collet's round capacity therefore does not prove that bar stock can pass through the installed closer. Haas HMDT; Haas AC-25.

Axial location, force and accuracy

Pullback closing can shift the workpiece axially as it grips and retracts. Royal describes dead-length actuation as addressing that movement for length control. Royal, pullback versus Accu-Length discussion.

Haas specifies up to 3,000 lbf (13,345 N) of draw force and 0.030-inch (0.76 mm) travel for the AC-25, with drilling and light milling as stated applications. These are closer-specific figures. Axial draw force is not a universal radial gripping force, permissible cutting torque or spindle-speed limit. Haas AC-25.

Accuracy claims also have conditions. Hardinge's special-accuracy 5C round-collet claim is 0.0002-inch maximum total indicator runout, held in a Hardinge Super-Precision spindle, for sizes over 3/16 inch through capacity, measured 1 inch from the collet face. This is not a guarantee for an arbitrary chuck, spindle or measurement location. Hardinge 2348J, printed page 4.

Step and expanding variants

Royal's 5C step and expanding offerings illustrate the latter two forms. Its expanding heads are machinable to the required size; its step collets close on the 10° taper rather than the head outside diameter. These are distinct products, not operating modes of an ordinary round-bore collet. Royal, 5C Emergency Step & Expanding Collets, undated page.

Worked example: 25 mm stock in a 1-inch collet

This original unit-conversion example assumes round stock measuring exactly 25.00 mm and a conventional collet marked 1.000 inch. It considers diameter mismatch only, without predicting grip force or accuracy.

Nominal collet diameter = 1.000 × 25.4 = 25.400 mm
Diameter mismatch      = 25.400 − 25.000 = 0.400 mm
Mismatch in inches     = 0.400 / 25.4 = 0.01575 in

The mismatch is about 3.15 times the 0.005-inch figure discussed above. Although both dimensions are commonly used for roughly one-inch stock, they are materially different for this spring-collet application. A hypothetical 25 mm nominal bore removes that nominal mismatch; it does not establish acceptance of the stock's actual tolerance, roundness, surface condition or gripping length.

The catalog capacity is a family maximum, not the closure range of one collet.

Coverage limits

These references establish selected product dimensions and operating distinctions, not universal interchangeability or an approved workholding setup. No common maximum rpm, actuation pressure, minimum gripping length, cutting load or unsupported bar length is established here. Installed chuck and closer design, mating threads, workpiece geometry and measured assembly runout remain consequential limitations.

For related concepts, see collet chucks and Cutting tools and tooling references.