M4x18 Socket Dog Point Set Screw: Holding Power Explained
By Products for bench top machinists | LittleMachineShop.com | Published: 2026-11-01
Category: Product Reviews
A dog point set screw solves shaft slip and collar alignment better than a cup point. Here's how to diagnose holding problems and when an M4x18 socket dog point is the right fix.
Quick answer
If a pulley, collar, or handwheel keeps slipping on a shaft, switch to an M4x18 socket dog point set screw. The dog point seats into a drilled dimple without raising a burr, so it holds alignment and removes cleanly.
Why a dog point holds better than a cup point in soft shafts
A cup point digs into the shaft and creates a raised burr that makes later removal difficult and can throw off concentricity. A dog point enters a drilled dimple and bears on the flat bottom, so the clamping force stays axial and the shaft stays true. That matters on small bench machines where a 0.05 mm burr can show up as runout.
The trade-off is preparation: you must drill a dimple at the exact contact point. Without that dimple, a dog point has less grip than a cup point because its flat nose cannot bite into the shaft.
When an M4x18 is the right length and when it is not
The 18 mm length suits collars and hubs with a wall thickness that leaves enough thread engagement without the screw protruding into the bore. If your component is thinner than about 10 mm, an 18 mm screw may bottom out or stick out; choose a shorter length instead. If the hub is thicker, verify that at least 1.5 times the thread diameter (6 mm) engages the threads.
For very thin collars or tight spaces, a cup point or flat point in a shorter length is often the better choice because it does not require a deep dimple.
Set screw vs grub screw: the naming does not change the fit
In North America the term set screw is standard; in the UK and Australia the same fastener is often called a grub screw. The M4x18 socket dog point set screw is the same part regardless of label. What changes is the point style and drive: socket drive accepts a hex key for higher torque than a slotted head, which reduces the chance of cam-out on small M4 threads.
Diagnose your set screw holding problem
- Symptom: collar or pulley slips under load: Check whether the current screw has a cup point that has already burred the shaft. If so, remove it, file the burr flat, and drill a dimple for a dog point screw. A burred shaft will loosen any screw; fix the shaft surface first.
- Likely cause: wrong point type for the application: If the shaft is hardened or you cannot drill a dimple, a dog point will not hold. Use a cup point or a shaft collar with a clamping screw instead. Dog points need a dimple; without one, choose a different point style.
- Corrective action: install an M4x18 socket dog point set screw: Drill a dimple 0.5 mm deeper than the dog point height, align the collar, and tighten the socket screw firmly with a hex key. Do not overtorque; M4 threads strip easily in aluminum hubs. Stop if the hex key starts to flex or the screw feels soft; you may be stripping the thread.
- When to stop or choose another option: If the hub wall is under 10 mm, switch to a shorter set screw. If the shaft is under 4 mm diameter, use an M3 screw instead. If you need frequent adjustments without tools, consider a thumb screw. Match screw length to hub thickness and shaft diameter before ordering.
Product facts
- Set Screw, M4x18, Socket Dog Point: M4 thread, 18 mm length, dog point, socket drive. The dog point seats in a drilled dimple for alignment, while the socket drive lets you apply reliable torque with a hex key.
Set Screw, M4x18, Socket Dog Point
