Set Screw Size and Type Chart: Flat Point, Cup Point & Dog Point

Reviewed by the ScrewBoltSize Editorial Team

You're trying to tighten a pulley that keeps slipping on a motor shaft, or you've got a door knob that spins freely because its set screw backed out. The hardware drawer has a handful of small headless screws with no markings — and you're not sure which point type you need, what size fits, or how tight to run it. This guide covers all five point types, their size charts, and the selection logic to get it right the first time.

What Is a Set Screw?

A set screw (also called a grub screw) is a fully threaded, headless fastener. Unlike a conventional bolt, there's no head extending above the surface — the screw threads flush with or below the face of the hub when tightened. This makes them ideal for applications where the fastener would otherwise snag on rotating parts.

Set screws thread into a tapped hole in the hub. When tightened, the tip contacts the shaft — either biting in, clamping, or engaging a groove depending on the point type. The holding method matters: choose wrong and the shaft walks free.

The Five Point Types

Cup Point

The most common set screw point. A sharp circular rim at the tip bites into the shaft surface when tightened, creating a small circular groove. This provides high axial and rotational holding force without fully penetrating the shaft.

Use when: General-purpose shaft retention. Door hardware, pulleys, handwheels, encoder wheels, HVAC damper controls. Compatible with steel, aluminum, and brass shafts.

Flat Point

A completely flat, blunt tip. Instead of biting in, it clamps against the shaft surface through pure compressive force. Holding power is lower than cup point, but it causes zero surface damage.

Use when: The shaft is hardened (cup point can't bite in anyway), when you need to reposition components along the shaft without leaving damage, or when a highly finished or plated shaft must not be marred. Common in precision instruments and positioning fixtures.

Dog Point (Pilot Point)

Has an extended cylindrical nose below the threaded portion that inserts into a mating hole or groove in the shaft. The nose provides precise axial location and prevents relative axial movement between hub and shaft.

Use when: The shaft has a machined groove, flat, or hole for the screw to engage. Motor shaft couplings, handwheels with keyways, and any application requiring positive axial location. Dog point set screws must not be used on plain (un-grooved) shafts — the nose will simply press against the surface with very little engagement.

Cone Point

A sharp conical tip designed to penetrate the shaft surface deeply, creating a strong permanent lock. Provides the highest holding force of any point type.

Use when: Permanent or semi-permanent assemblies where disassembly is rarely needed. High-vibration industrial applications. Hard materials where cup point doesn't grip adequately. Note: cone point damages the shaft significantly and repositioning is essentially impossible.

Oval Point

A rounded, dome-shaped tip. Similar to flat point in that it doesn't bite or penetrate, but the curved surface allows for slight angular misalignment between the screw and shaft axis. Used on finished, lapped, or extremely hard shafts where even flat-point contact stress is a concern.

Set Screw Size Chart — Metric

Torque values are for zinc-plated alloy steel (12.9 class equivalent) into a steel shaft, dry. Reduce by 25% for aluminum shafts to avoid stripping the hub threads. Minimum engagement depth is 1× screw diameter for cup point in medium-hardness steel.

Set Screw Size Chart — Imperial

How to Identify an Unknown Set Screw

If you're looking at a set screw already installed (or one that fell out), here's the diagnostic sequence:

1. Measure the OD. Use calipers across the threads. Match to the nearest nominal diameter in the tables above. A reading of 5.8–6.0 mm → M6. A reading of 0.245–0.255" → 1/4".
2. Check the thread pitch. Count threads over 10 mm of length for metric (e.g., 10 threads = 1.0 mm pitch). For imperial, count threads per inch. A thread pitch gauge makes this step instant.
3. Identify the drive. If a standard hex key fits, it's hex socket. If it's slotted, it's an older style — still used in door hardware. Torx socket set screws exist but are less common.
4. Identify the point type. Look at the tip: flat = flat point, small sharp ring = cup point, cylindrical nose = dog point, sharp cone = cone point.

Point Type Selection Guide

Thread Locker: When and Which Grade

Set screws in vibrating assemblies — motors, power tools, HVAC fans — will back out over time without thread locker. Here's the simple rule:

• Loctite 242 (blue, medium): Use for most set screw applications. Removable with standard hex keys and a firm push. Safe for aluminum hubs.
• Loctite 243 (blue, oil-tolerant): Same strength as 242 but cures even in the presence of light oil. Good for engine and gearbox applications.
• Loctite 271 (red, high-strength): Permanent. Requires heat (250°F+) to break loose. Only use on non-removable assemblies where vibration is severe and disassembly is not expected.

Common Set Screw Failures and Fixes

Shaft slipping inside the hub (rotational)

If the shaft spins inside the hub even with the set screw fully seated, the cup point isn't engaging. Check: Is the shaft soft enough for a cup point to bite? Is the set screw long enough to fully reach the shaft? Is the screw already worn or rounded at the tip? Replace with a new set screw, apply Loctite 242, and re-torque to spec.

Shaft walking axially

Cup point set screws resist rotation better than axial force. If the shaft slides along its axis, you need a dog point engaging a groove, a second set screw 90° apart, or a keyway and key combination.

Set screw backing out

Always use Loctite 242 on set screws exposed to vibration. Verify the thread engagement is at least 1× the screw diameter. Verify the hex key fit — rounded-out sockets let the key cam out during torquing and result in under-torqued screws.