Truss Head (Mushroom Head)
Direct Answer
Truss Head screws (also known as Mushroom Head / Extra-Wide Pan) feature an extra-wide, low-profile domed head with a large-diameter flat bearing underside. Designed to span large clearance holes and clamp thin sheet metal without tearing or requiring external flat washers, they are widely used in metal building framing and cabinet door hardware.
Source: ASME B18.6.3 / DIN 7981 Variant
Specs
| Standard Specifications | ASME B18.6.3 / IFI Standards |
| Head Diameter Ratio | Extra-wide base ($D_k \approx 2.2\times$ to $2.5\times$ shank diameter) |
| Head Height Profile | Ultra-low curved dome (flatter and wider than standard pan head) |
| Bearing Surface | 100% Flat horizontal bearing surface with maximum surface contact area |
| Common Drive Recesses | Phillips (PH2), Square (Robertson #2), Combo, Slotted |
| Primary Applications | Thin sheet metal ducting, electrical junction boxes, cabinet drawer slide tracks |
Sheet Metal Clamping and Washer Elimination
When fastening thin materials (such as HVAC aluminum ducting, sheet metal appliance skins, or electrical panels), standard small-diameter screw heads can punch through or deform the hole under tension. The extra-wide rim of the truss head spreads the clamping load over double the surface area, acting as a built-in flat washer.
Drawer Slide Track Clearance
In cabinetry, #8-32 truss head screws are standard for mounting ball-bearing drawer slides: the low-profile dome clears moving ball bearings inside the track without binding.