Set screws

Unbrako's inch cup-point example lists 0.1250–0.1270 in hex socket size and 0.114–0.125 in point diameter. The 0.125 in minimum key engagement applies at or above the 0.25 in shortest optimum nominal length in that row. Check the point, drive and threaded engagement separately before using holding-power data from a shaft-and-collar test. Unbrako, printed p. 20 / PDF p. 22.

Scope and contact mechanism

A headless socket set screw, or grub screw, develops contact at its point as it advances through the tapped hole. Unbrako Engineering Guide, printed pp. 18 and 22 / PDF pp. 20 and 24.

In a shaft and collar, the point contact and receiving thread provide the load path.

Point forms

The Unbrako guide illustrates these forms as separate geometries. Its application descriptions relate them to the mating material, relative hardness and frequency of adjustment; they do not establish universal compatibility or damage-free contact. Unbrako, printed pp. 20–21 / PDF pp. 22–23

The geometry sketches are on printed p. 18 / PDF p. 20, with application descriptions on printed p. 21 / PDF p. 23. These descriptions are not shaft-preparation or installation instructions. No common penetration depth, reuse count or surface-damage limit follows from the point name.

Supplier application descriptions are not uniform. Holo-Krome's socket-set-screw page describes its cup point for soft shafts and cautions against hardened shafts. Unbrako's plain-cup description includes hardened shafts. The inspected evidence does not reconcile these product-specific statements into a single shaft-hardness rule. Holo-Krome, Cup Point description, Unbrako, printed p. 20 / PDF p. 22

Thread, drive and length are different dimensions

Unbrako's inch table separately identifies nominal screw diameter, threads per inch and socket geometry. Its nominal 1/4-inch row lists 20 threads/inch under UNRC and 28 under UNRF; the notes identify thread Class 3A. Those thread designations do not specify the point form or the length of the screw. Unbrako, printed pp. 18–19 / PDF pp. 20–21

The same source distinguishes overall screw length from key engagement. Its caution states that shorter-than-listed minimum-stock-length cup-point screws may not have enough socket depth for full key capability. Thus the availability of a hexagonal recess does not establish a common engagement depth across all lengths. The guide also makes its recommended seating-torque columns conditional on nominal minimum length; no seating-torque value is adopted here. Unbrako, printed p. 19 / PDF p. 21

Bounded manufacturer dimensional example

Holo-Krome product standard HK.USA.SSS.CP.BO, REV-01, January 21, 2011 describes US-manufactured socket set screws with cup point and black-oxide finish. Its manufacturer page links the document as inch product specifications. The following is its nominal 1/4-inch size row, not an individual part-number drawing or a current production-lot certification. Holo-Krome product page, product standard, p. 1

All example fields and the length-dependent T footnote are on the one-page Holo-Krome standard. Overall length L, point diameter and socket engagement have different meanings. In particular, the listed T is not an unconditional property of every short screw of the same nominal diameter. No drawing angle or dimensional field from another point form is transferred to this example.

Materials and specification scope

The Unbrako guide's inch set-screw notes distinguish alloy steel associated with ASTM F912 from stainless steel associated with ASTM F880. They list Rockwell C45–53 for the alloy-steel family and a separate range, Rockwell B96 to C33, for stainless steel. These are the guide's product-family statements, not hardness values for the shaft or a universal set-screw grade. Unbrako, printed p. 19 / PDF p. 21

The Holo-Krome example instead identifies its own product standard, finish and referenced requirements. A common material-family name does not demonstrate identical finish, contact behavior or conformity to a particular edition. The inspected sources do not establish a general corrosion lifetime, temperature limit or stainless/alloy-steel interchangeability.

DIN Media's publisher listing identifies ISO 4029:2026-02, titled Fasteners — Hexagon socket set screws with cup point, as replacing ISO 4029:2003-12. This is a bounded edition/identity reference. It does not show that an older manufacturer document or an unspecified product conforms to the 2026 edition. No dimensions or mechanical requirements from the full ISO standard are reproduced here. DIN Media, ISO 4029 listing

Holding-power evidence and its limits

Unbrako's holding-power section concerns cup-point screws seated at its stated installation torques in a shaft-and-collar assembly with Class 3A screw threads in Class 2B tapped holes. In this static test, holding power is the minimum load producing 0.010 in relative movement of shaft and collar. Axial holding power is reported as a force in pounds; torsional holding power is reported as a resisting moment in inch-pounds. The torsional result is distinct from the seating torque used to install the screw. Explanatory synthesis: this is a specified-displacement criterion, not an ultimate-fracture load or a guarantee of zero relative movement. Unbrako, printed p. 22 / PDF p. 24

The paragraph states that the test shafting was hardened to Rockwell C15, while the table heading labels shaft hardness Rc 15 to Rc 35. Both statements are present on the inspected page. The source does not explain their relationship there; this draft does not collapse them into a single verified test condition. The inspected test description does not identify a shaft alloy grade or a surface-finish value. The page also labels its tabulated strengths as typical. No numerical holding-force or torsional-capacity result is transferred to an unspecified shaft, collar, screw or service load. Unbrako, test description and table header, printed p. 22 / PDF p. 24

The guide separately discusses torsional, axial and vibrational holding behavior and identifies relative screw/shaft hardness and point penetration as influences. Its static shaft-and-collar data do not establish a generic resistance to vibration, repeated adjustment, slip, bending or shaft damage. Unbrako, printed p. 20 / PDF p. 22

Coverage and source versions

Source retrieval date: 2026-10-30 PDT, America/Los_Angeles. Definition clarification reviewed 2026-10-31 PDT against the retained primary-source pages. These dates are distinct from source publication or revision date.

• Unbrako, Socket Products Engineering Guide: the retrieved manufacturer PDF has 88 pages. Printed pp. 18–22 correspond to PDF pp. 20–24 and were visually inspected, including sketches, table headings and footnotes. A printed issue date/revision was not established from those sections. PDF creation/modification metadata are not treated as publication dates. The guide is not represented as a current controlled part drawing; the entire catalogue was not reviewed.
• Holo-Krome HK.USA.SSS.CP.BO: the full one-page document and drawing were visually inspected; its printed identification is REV-01, January 21, 2011. Its presence on the retrieved manufacturer page does not establish that this is the latest production specification.
• Holo-Krome HTML and DIN Media listing: publication/revision date for the HTML product text is unstated; the DIN listing explicitly identifies the February 2026 ISO issue. Website footer dates are not publication evidence.

No full ASME, ASTM or ISO standard was inspected. The cited material does not qualify a customer's mating component, setting procedure or finished assembly. There is no universal tightening-torque, holding-force, fatigue, damage, life or reuse value in this draft.

Related reference

Hardware and component references supplies adjacent process context; it does not qualify these screws or their mating components.