303 Stainless Steel Knurled Thumb Screws With Small Head M3/M4x6~16mm Hand Screw

M3 screws have a 3 mm nominal thread diameter and are suited for lightweight panels, PCB standoffs, and small enclosures where load is minimal. M4 screws have a 4 mm diameter and handle moderately higher clamping loads, making them a better fit for thicker aluminum panels, fixture plates, and structural access covers. If your tapped hole is already cut, match the thread diameter exactly — M3 and M4 are not interchangeable.

These screws follow standard ISO metric coarse thread pitches: M3 uses a 0.5 mm pitch and M4 uses a 0.7 mm pitch. These are the most common pitches for M3 and M4 fasteners, so they will mate with the vast majority of metric-tapped holes in aluminum, steel, and plastic components without any special consideration.

303 stainless steel provides good general corrosion resistance and performs well in indoor environments and applications with occasional moisture exposure. It is not recommended for continuous immersion in saltwater or highly corrosive chemical environments — for those conditions, 316 stainless steel would be a more appropriate choice. For typical electronics enclosures, lab equipment, and indoor fixtures, 303 is a practical and cost-effective option.

As a general guideline, the engaged thread length should be at least 1× the thread diameter for steel or aluminum, and 1.5–2× for softer materials like plastic. For a 1.5 mm aluminum panel with a standard nut on the back, the 6 mm length is typically sufficient. For thicker panels or when threading directly into a tapped block, choose a longer variant (10 mm or 16 mm) to ensure adequate thread engagement. Always account for panel thickness plus any washer or nut stack height when selecting length.

Yes, in applications where tool-free access is acceptable. The thread diameter and pitch are identical to standard metric socket head cap screws in the same size, so they will thread into the same tapped holes. The key difference is the head style — the knurled cylindrical head is larger in diameter than a typical socket head and is not designed for high-torque power tool installation. Use these where hand-tightening force is sufficient for the joint.

For prototyping or single-unit builds, the 1 PCS or 3 PCS options let you validate fit before committing to larger quantities. For small-batch production runs of 10–50 units, the 10–50 PCS packs offer a practical balance. For ongoing production or stocking purposes, the 80–200 PCS packs reduce per-unit cost. Because these screws are sold by exact size and quantity variant, you can mix and match different size variants in separate orders to cover your full BOM without over-stocking any single size.