Hollow Wall Anchor (Molly Bolt)
Direct Answer
The Hollow Wall Anchor (Molly Bolt, patented by George F. Croessant in 1934) is an all-metal expansion fastener featuring a slotted steel sleeve that permanently crimps into 4 outward-flaring legs behind hollow drywall or plaster. Unlike toggle bolts, the anchor sleeve remains permanently clamped to the wall, allowing the machine screw to be removed and re-inserted repeatedly.
Source: US Patent 1,988,277 (Molly Corporation) / ASTM Fastener Standards
Specs
| Sleeve Material | Pre-slotted zinc-plated cold rolled steel sleeve with barbed anti-spin collar |
| Internal Machine Screw Thread | M4, M5, M6 (Metric) or 1/8", 3/16", 1/4" (Imperial) |
| Grip Range Sizing | Short (1/8" to 3/8" wall thickness), Medium (3/8" to 1/2" drywall), Long (5/8" to 1" double-drywall/lath) |
| Permanent Retention | Yes (Sleeve stays permanently crimped into the wall when screw is removed) |
| Setting Method | Tightening the screw with a screwdriver or using a specialized manual Molly setting plier tool |
| Safe Shear Load (1/2" Drywall) | Up to 50 lbs (23 kg) shear per anchor |
The Molly Crimping Mechanism
When installed into a hole matching the sleeve outer diameter, two sharp prongs under the collar bite into the drywall face to prevent spinning. As the central machine screw is tightened, the threaded nose of the sleeve is drawn backward, causing four pre-scored steel side ribs to buckle outward into a rigid 4-point cross bracket pressed against the rear drywall surface.
Removable Screw Advantage
The decisive engineering advantage of the Molly bolt over a spring toggle bolt is serviceability: because the collapsed metal sleeve remains locked to the wallboard, the machine screw can be unscrewed to paint walls, clean fixtures, or swap electrical brackets without losing the anchor.