M12-1.75 x 50mm Low Head Socket Cap Screws: Fit and Torque

By Mutual Screw & Supply | Published: 2026-11-01

Category: How-to Guides

Learn how to install M12-1.75 x 50mm low head socket cap screws correctly. Get fit checks, torque guidance, and avoid common mistakes with partially threaded Class 8.8 screws.

Quick answer

To install M12-1.75 x 50mm low head socket cap screws, first verify that the low head height clears your assembly and that the 50mm length gives full thread engagement in the tapped hole. Then clean the threads, lubricate if specified, and torque in stages using a torque wrench with the correct hex bit.

Why the low head profile changes your fit check

A low head socket cap screw has a shorter head height than a standard socket cap screw, which saves clearance in tight spaces but also reduces the bearing area under the head. That means the surface you clamp must be flat and strong enough to distribute the load without deforming. Check that the head does not bottom out in a counterbore and that the socket remains accessible for the hex key.

Thread engagement and partially threaded length

These screws are partially threaded, so the unthreaded shank passes through the clearance hole before the threads engage. Confirm that the thread length is sufficient for your material: in steel, aim for at least one diameter of engagement (12mm); in aluminum or softer materials, more engagement may be needed. If the shank is too long for the clamped parts, the screw may not clamp firmly even at full torque.

Torque values for Class 8.8 low head screws

Class 8.8 alloy steel provides good strength, but low head screws have less head material than standard socket heads, so the safe torque can be lower. Always follow the machinery manufacturer's specification if available. If not, use a torque value for M12 Class 8.8 socket cap screws reduced by about 10–20% as a starting point, and verify joint integrity. Lubrication affects torque-tension relationship: dry threads need more torque for the same preload, while lubricated threads need less. Be consistent.

Installation steps for M12-1.75 x 50mm low head socket cap screws

Verify clearance and head fit: Place the screw through the clearance hole and check that the low head sits flush and does not interfere with nearby components. Ensure the socket is accessible for the hex key. A low head saves space but can bottom out in shallow counterbores—check depth first.
Check thread engagement: With the joint assembled, confirm that the threaded portion engages at least 12mm (one diameter) into the tapped hole. For softer materials, aim for 1.5–2 times the diameter. Partially threaded screws may need a longer thread length if the clamped stack is thick.
Clean and lubricate threads: Remove debris from both male and female threads. Apply the lubricant specified for your application, if any. Use a wire brush or compressed air to clean. Consistent lubrication is critical for achieving correct preload with torque.
Start threading by hand: Thread the screw in by hand until it seats. This prevents cross-threading and ensures the screw is not binding. If it binds, back out and inspect threads—forcing it can damage the tapped hole.
Torque in stages: Using a calibrated torque wrench and the correct hex bit, tighten to 50% of target torque, then 75%, then 100%. For multiple screws, tighten in a cross pattern. Staged tightening distributes clamp load evenly and reduces relaxation.
Record and verify: After torquing, mark the screw head and mating surface to allow visual inspection. Re-check torque after the first thermal cycle or 24 hours of service. Low head screws can relax; a re-torque check catches settling.

Product facts

M12-1.75 X 50mm Socket Cap Screws | Low Head Hex Socket Drive | Partially Threaded | Class 8.8 Alloy Steel (200 / Pkg.): M12-1.75 x 50mm socket cap screws made from Class 8.8 alloy steel with hex socket drive and partially threaded design. Class 8.8 gives reliable strength for machinery and tooling, while the partial thread suits through-hole clamping.
M12-1.75 X 50mm Socket Cap Screws | Low Head Hex Socket Drive | Partially Threaded | Class 8.8 Alloy Steel (200 / Pkg.)