Metal Roofing Bolt & Nut

What gutter bolts (roofing bolts) are

A roofing bolt is a short machine thread bolt with a low, domed head (the trade often calls them mushroom head bolts) and a hex nut. The domed head sits smoothly on sheet metal and the combination Phillips and slotted drive takes either a Phillips or a flat screwdriver, while you hold the nut with a spanner. Each bolt is sold with its nut.

Roof plumbers know them as gutter bolts: they bolt through overlapping sheet metal, so they are used for joining gutter lengths, stop ends and downpipe fittings, and for fixing flashings, sheet metal parts and signs where a bolt and nut is wanted instead of a screw or rivet.

Roofing bolt sizes

Every size and length we carry, imperial first, then metric. Select a row to open that bolt in the selector.

Imperial or metric, and which length

• •Imperial (3/16, 1/4 and 5/16 inch): listed to ANSI B18.6.3. 3/16 inch comes from 1/4 to 3 inches long, 1/4 inch from 3/8 to 3 inches and 5/16 inch from 1/2 to 3 inches.
• •Metric (M5 and M6): fully threaded, listed to JIS B1111. M5 comes in 12, 16, 20 and 25mm and M6 from 10 to 50mm.
• •The bolt and nut are sold together, so the thread always matches. Do not mix imperial bolts with metric nuts or the other way round.
• •Length: the total thickness of everything being joined, plus a full nut and a thread or two past it. Joints in thin sheet need only the short lengths; the longer ones suit brackets, signs and thicker parts.

How to fit a gutter bolt

1. Line up the parts and drill a clearance hole a little bigger than the bolt: 3/16 inch is 4.76mm, 1/4 inch is 6.35mm, 5/16 inch is 7.94mm, M5 is 5mm and M6 is 6mm.
2. On a gutter joint, put the gutter or roofing maker's sealant in the joint first, as their instructions say.
3. Push the bolt through from the side that will be seen, so the domed head sits on that face.
4. Run the nut on and hold it with a spanner or nut driver while you turn the head with a Phillips or flat screwdriver. Tighten until the sheets pull together; do not crush thin sheet.
5. Wipe off excess sealant and swarf: steel drilling swarf left on a roof or gutter rusts and stains.

Zinc plated: where they last, and when to use stainless

These bolts and nuts are zinc plated. Hobson's finish comparison rates zinc plating (about 5 microns) as low corrosion resistance, for indoor and non-corrosive environments. Gutters and flashings are outdoors in the weather, which Hobson's corrosion guide treats as exposed, where it points to stainless steel or hot dip galvanised. So zinc plated gutter bolts will show rust sooner than the gutter, especially near the coast.

For exposed or coastal work, first check the gutter or roofing maker's guidance on which fastener materials suit their sheet, since some metals do not mix. Where it allows stainless, our machine screw range has 304 stainless mushroom head screws in 3/16 inch, 1/4 inch, M5 and M6 and 316 round head screws in 3/16 and 1/4 inch, with stainless hex nuts.

Gutter bolts in Adelaide

Allmat supplies roofing bolts and nuts, roofing screws, sealing washers and rivets to roof plumbers, roofers, builders and trade across Adelaide and South Australia. Add them to a quote with the rest of your roofing list.

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