304 Stainless Steel Countersunk Bolts M3-M20 Hex Socket Flat Head Screws

Countersunk bolts feature a conical head that sits flush with or below the workpiece surface when installed into a pre-machined countersink hole. [Standard number to be confirmed: ANSI B18.3 (hex socket) or B18.6.3 (Phillips)]

Unlike socket head cap screws, countersunk bolts eliminate surface protrusions, reducing fluid drag and interference risks. Compared to square head bolts, they deliver concealed installation for precision aesthetic surfaces and tight-clearance applications.

• A2-70 (304 equivalent): 700 MPa tensile strength, general corrosion resistance, indoor/light outdoor environments

• A4-80 (316 equivalent): 800 MPa tensile strength, molybdenum-enhanced chloride resistance, marine/chemical applications

• A2-50/A4-50: Cold-worked, moderate strength, cost-sensitive projects

• Plain (Uncoated): Native stainless passivation layer, cleanroom/medical equipment compatible

• Electropolished: Ra ≤0.8 μm surface roughness, eliminates micro-cracks, medical/semiconductor preferred

• PTFE Coating (Xylan®): 0.05-0.10 friction coefficient, anti-galling, 260°C service temperature

• Uncoated SS: Maintains intrinsic corrosion resistance, avoids galvanic coupling risks

• Diameter: M3-M24 (coarse/fine thread optional)

• Length: 6-200mm (full thread/partial thread)

• Drive Type: Hex Socket / Phillips / Slotted • Head Angle: 90° countersink (standard) / 82° (imperial)

• Diameter: #4-1″ (UNC/UNF thread)

• Length: 1/4″-8″ • Drive Type: Hex Socket / Phillips / Slotted • Standard: ANSI B18.3 (hex socket) / B18.6.3 (Phillips)

Scenario 1: Precision Sheet Metal Enclosures Square head bolt protrusions disrupt stackable shipping. Countersunk bolts enable zero-gap panel mating with M4-M6 and A2-70, achieving IP65 enclosure ratings.

Scenario 2: Automated Conveyor Systems Socket head screw protrusions snag conveyed materials. Countersunk bolts’ flush installation eliminates interference points; PTFE coating reduces friction against polymer slide blocks, extending maintenance intervals.

Scenario 3: Marine Decking Square head bolt protrusions create trip hazards and water pooling. Countersunk bolts with A4-80 and electropolish maintain surface integrity in salt spray, meeting USCG safety codes.

Situation: A precision medical equipment manufacturer used standard socket head cap screws for CT scanner housings. Screw head protrusions caused surface dents during stacked shipping, and disinfectant pooled around protrusions, creating corrosion spots.

Task: Required a fully flush-mount, hydrogen peroxide-resistant fastening solution compliant with FDA 21 CFR 888.30.

Action: Supplied A2-70 electropolished countersunk bolts, M6×20mm, 90° head angle matching countersinks, Ra ≤0.4 μm surface finish, with material certificates and batch traceability codes.

Result: Eliminated surface denting and corrosion risks; cleaning cycle reduced by 30%; equipment surface rating upgraded to Class A (reported).