80/20 Flanged Button Head Socket Cap Screw - 5/16-18 x .687" (P/N 3330)

The bolt that goes with the T-nut. Zinc-plated, flanged button head, 5/16-18 × .687" — 80/20 part number 3330.

The flange is the point. A flanged button head spreads its clamping load across a wider area than a plain button head, which stops the bolt from pulling through a bracket hole and stops the head from digging into soft aluminum as you torque it.

The .687" length is matched to a standard bracket thickness plus a T-nut in a 15 series slot. Longer bolts bottom out inside the slot before they clamp; shorter ones do not get enough thread engagement. This is the one that is right.

What it is for

• Bolting brackets, plates and accessories to 15 series 80/20 extrusion, paired with a 5/16-18 T-nut.
• Anywhere a plain button head would dig into or pull through the bracket.
• Interior framing and protected locations — for exposed exterior use, consider the black stainless version.

Compatibility

The 15 series is the 1.5 inch profile — the size almost every van roof rack and interior framing system is built from. If your extrusion measures 1.5 in across the face and takes a 5/16-18 fastener, this is your hardware.

Specifications

What's included

• (1) 5/16-18 × .687" zinc flanged button head socket cap screw

Working with it

A quality hex key that actually fills the socket is worth more than any other tool on a rack build. Rounded-out sockets on a roof rack, three years and one winter later, are the reason people cut brackets off with an angle grinder.

• Use a properly fitting hex key or bit — a sloppy one rounds the socket.
• Do not overtighten. You are clamping into an aluminum slot, and there is a point past which more torque only deforms the extrusion.
• Re-check torque after the first long drive. Vibration finds every fastener.
• For exterior use in a salted climate, the black stainless equivalent (3607) has better corrosion life.

Questions we get asked

How do I know if my extrusion is 15 series?

Measure across the flat face of the profile. A 15 series extrusion is 1.5 in wide (or a multiple — 1.5 × 3.0, and so on) and the T-slot takes a 5/16-18 fastener. If your rack came from Unaka, 80/20 Inc., or most van rack makers in North America, it is 15 series.

How many should I order?

Count your joints, then add 20%. Rack hardware is the cheapest thing in a build and the most annoying thing to run out of halfway through a Saturday. We have never once regretted having spare T-nuts in the drawer.

Why .687" and not a rounder number?

Because it is matched to the geometry of the 15 series slot plus a standard bracket. It is long enough for full thread engagement into a T-nut and short enough not to bottom out inside the slot.

Zinc or stainless?

Zinc is fine indoors and under a rack fairing. If the bolt head sits exposed on a roof rack through a salted winter, spend the extra on the black stainless version.

Pairs well with

• Van roof rack, ladder and 80/20 hardware

Sold and shipped by Campervan Parts R Us, the parts counter of Noke Van Co. — a working van conversion shop in Roanoke, Virginia. If you are unsure whether this fits your van, email us the year, model and wheelbase and we will check it against a build sheet before you order.