Expansion Wall Plugs vs. Molly Bolts
Comparing 2 standards across 13 specifications. 13 key differences identified.
The Plastic Expansion Wall Plug (Rawlplug / Fischer S-Plug / Dowel) is a split cylindrical nylon or polyethylene sleeve inserted into a pre-drilled masonry hole. When a wood or sheet metal screw is driven inside, the tapered internal profile wedges the split halves outward, generating strong radial expansion friction against solid concrete, brick, or stone.
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.
Specification Comparison Table
13 Parameters| Parameter / Spec | ||
|---|---|---|
|
Standard Sizing Convention
|
Outer Diameter × Length (e.g. 6×30 mm, 8×40 mm, 10×50 mm) | — |
|
Standard Drill Bit Sizing
|
Drill bit diameter matches plug outer diameter exactly (e.g. 6 mm plug = 6.0 mm masonry bit) | — |
|
Standard Substrates
|
Solid concrete, solid clay brick, natural stone, aerated block | — |
|
Expansion Mechanism
|
Screw core forces 2 or 4 split ribbed plastic wings radially against hole walls | — |
|
Anti-Rotation Features
|
Molded longitudinal external ribs / anti-spin fins that bite into the masonry borehole | — |
|
Common Safe Shear Load (Concrete)
|
6mm plug: ~30–50 kg (65–110 lbs) / 8mm plug: ~70–100 kg (150–220 lbs) | — |
|
Primary Applications
|
Wall shelves, curtain rods, electrical panels, bathroom mirrors, light fixtures | — |
|
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 |