Button Head Socket Cap Screw

Button Head Socket Cap Screws — Low-Profile, Alloy and Stainless Steel

Shop Button Head Socket Cap Screws

Button head socket cap screws — also called button head Allen screws, button head cap screws, or BHCS — are distinguished by a wide, low-profile dome head with an internal hex socket drive. Compared to a standard socket head cap screw, the button head is shorter in height but wider in diameter, spreading the bearing load over a larger surface area while keeping the fastener profile as low as possible. The smooth, rounded top has no sharp edges, which reduces snagging on cables, clothing, and adjacent components.

When to Use Button Head vs. Socket Head Cap Screws

Button head socket cap screws are not a direct substitute for socket head cap screws (SHCS) in high-load structural joints. The button head has a reduced socket depth relative to the thread size, which limits the torque that can be applied before the socket rounds out. ASME B18.3 defines button head cap screws as a low-strength alternative to standard socket head cap screws. Use them where clamp load requirements are light to moderate and aesthetics, low profile, or snag-free installation are the primary considerations. Verify load requirements before substituting button heads for SHCS in an existing assembly.

Alloy Steel Button Head Cap Screws

Alloy steel button head socket cap screws are heat treated, with tensile strength typically in the range of 150,000–170,000 PSI depending on manufacturer and size. They conform to ASME B18.3 for inch series. Standard finish is plain (bright) or black oxide. Alloy button heads are used in robotic assemblies, 3D printers and CNC equipment, machine guarding, jig and fixture components, and any application where the fastener head will be visible or frequently removed.

Stainless Steel Button Head Cap Screws

18-8 stainless steel button head socket cap screws are widely used in food service equipment, outdoor structures, marine hardware, and consumer products where corrosion resistance and a clean appearance are both required. The smooth dome profile resists buildup and is easy to wipe clean. Available in 18-8 (302/304) stainless for general corrosion resistance.

Metric Button Head Socket Cap Screws

Metric button head socket cap screws conform to ISO 7380 (alloy, Class 10.9) and are available in 18-8 stainless. Common metric sizes run from M3 through M12. The metric button head uses a larger hex socket relative to thread diameter than most inch-series versions, providing slightly better torque capacity in metric applications.

Frequently Asked Questions

Are button head socket cap screws as strong as socket head cap screws?
No — button head cap screws are rated as a lower-strength alternative under ASME B18.3. The shallower socket engagement limits maximum applied torque. Do not substitute button heads for socket head cap screws in structural or high-clamp-load joints without verifying load requirements.

What hex key size do I use for button head cap screws?
Button heads use smaller hex keys than SHCS of the same thread size. Common pairings: 1/4"-20 ? 5/32" hex key; 5/16"-18 ? 3/16"; 3/8"-16 ? 5/32" or 3/16" (verify by fastener). Metric: M5 ? 3mm; M6 ? 4mm; M8 ? 5mm; M10 ? 6mm. Always verify — undersizing risks socket rounding.

What is the difference between a button head and a pan head screw?
Both have a low, wide head, but they are driven differently. Button head cap screws use an internal hex socket (Allen key). Pan head screws typically use a Phillips, slotted, or Torx drive and are a machine screw form, not a socket cap screw. Button heads provide higher torque capacity and a cleaner top profile.

Can button head cap screws be used in a counterbore?
Yes — a shallow counterbore can seat the head flush or below the surface. However, the wide head diameter of a button head requires a larger counterbore than an equivalent SHCS. Verify counterbore dimensions against the fastener head diameter before machining.

Button head socket cap screws are often used alongside socket head cap screws in the same assembly — SHCS where high clamp load is needed, button heads where aesthetics or snag-free profile matters. Flat washers and lock washers pair naturally with both. For other socket fastener types — including flat head socket cap screws for countersunk applications and socket set screws for shaft locking — see the full Sockets category.