M24 Hex Head Cap Screws: Sizing and Strength Guide
By Mutual Screw & Supply | Published: 2026-10-23
Category: Buying Guides
Learn how to choose the right M24 hex head cap screw for your project. This guide covers sizing, threading, material, and practical selection rules.
Quick answer
For most M24 applications, choose a partially threaded 18/8 stainless steel hex head cap screw when you need corrosion resistance and a secure, wrench-driven fastening in machinery or equipment assembly.
Why thread length matters on a large-diameter bolt
An M24 bolt is a large-diameter fastener, so the choice between fully threaded and partially threaded directly affects clamping force and assembly ease. A partially threaded design leaves a smooth shank near the head, which reduces stress risers and allows the bolt to be tightened against a surface without galling threads.
The trade-off: a partially threaded bolt requires the mating part to have enough clearance for the unthreaded shank. If you are tapping into a blind hole or need maximum thread engagement in a shallow nut, a fully threaded option might be a better fit.
Material selection: 18/8 stainless steel
18/8 stainless steel (also called Type 304) offers good corrosion resistance for indoor and outdoor use, making it a common choice for food processing equipment, marine hardware, and general industrial fastening. It is non-magnetic and resists rusting in most environments.
The limitation: 18/8 stainless steel is not as strong as alloy steel grades like Class 8.8 or 12.9. If your application requires high tensile or shear strength—such as in structural steel connections or heavy load-bearing frames—you should consider a hardened steel bolt instead.
Decision rules for choosing an M24 hex head cap screw
- Check the thread pitch and length: M24 bolts have a standard thread pitch of 3mm. Confirm your nut or tapped hole matches this pitch. Measure the total bolt length (220mm in the example) and ensure the threaded portion is long enough for your material stack-up.
- Select partially threaded for most machinery assembly: If you are bolting two flanges or mounting a component where the bolt passes through a clearance hole before engaging threads, choose a partially threaded bolt. The smooth shank prevents thread damage during insertion and improves clamping consistency.
- Match material to environment and load: Use 18/8 stainless steel for corrosion resistance in wet, outdoor, or food-contact settings. Switch to a high-strength alloy steel bolt when the application demands higher tensile strength or resistance to fatigue under cyclic loads. Always verify the grade specification (e.g., 18/8, Class 8.8, Class 12.9) against your design requirements.
- Confirm drive compatibility: M24 hex head cap screws use a hex socket drive. Ensure you have the correct hex key or socket size (typically 17mm or 19mm, but measure the head across flats). A hex head allows higher torque without rounding compared to a Phillips or slotted drive.
Product spotlight
- M24-3 X 220mm Hex Head Cap Screws | 18/8 Stainless Steel | Partially Threaded (5 / Pkg.): M24-3 x 220mm hex head cap screws in 18/8 Stainless Steel, partially threaded, sold in packs of 5. The partially threaded shank reduces thread galling during tightening, and the 18/8 stainless construction resists corrosion in damp or wash-down environments.
M24-3 X 220mm Hex Head Cap Screws | 18/8 Stainless Steel | Partially Threaded (5 / Pkg.)
Who should use this M24 hex head cap screw
Best for
- Machinery and equipment assembly where corrosion resistance is a priority
- Outdoor or wash-down environments requiring 18/8 stainless steel
- Applications that benefit from a partially threaded shank to reduce galling
Not for
- High-strength structural connections where alloy steel grades are required
- Blind holes or shallow nuts that need full thread engagement along the entire bolt length
