Pin Torx Button Head Connector Nut

What a button head security barrel nut does

Hobson describes this barrel nut as a tamper proof security female connecting screw, used to replace a nut in timber and steel connections. It is a headed barrel with a female thread inside. The screw goes through the parts from one side, the barrel nut goes in from the other, and the two are tightened together, so both faces show a domed button head and no thread is left sticking out. The pin in the Torx drive gives a level of security to fixings in public areas.

Hobson also lists it as a decorative nut, for bridging and tightening gaps between two parts, and among its uses timber connections, park and playground equipment, furniture, balustrades and replacing the nut in a masonry fixing. Hobson publishes no load rating for these nuts, so fixings on balustrades, play equipment and anything that carries people or loads must be the rated fixings the equipment or structural designer specifies.

Security barrel nut sizes

Choose the thread to match the screw, then the length to suit the joint (see working out the screw length, below). Select a row to open that nut in the selector.

Matching pin Torx screws and bits

Hobson pairs its 3/8 UNC button barrel nut with the matching 3/8 UNC button head post Torx screw as a two-way security fitting. For these metric nuts it names no partner screw, but our pin Torx button head machine screws share the thread, the 304 stainless and the T size, so one bit or key fits both halves:

• •M5 barrel nut (T25): M5 button head pin Torx machine screws, 10 to 60mm long.
• •M6 barrel nuts (T30): M6 button head pin Torx machine screws, 10 to 50mm long.
• •M8 barrel nuts (T40): M8 button head pin Torx machine screws, 16 to 80mm long.
• •M10 barrel nuts (T45): M10 button head pin Torx machine screws, 16 to 50mm long.
• •3/8 UNC barrel nut (T45): 3/8 UNC button head pin Torx machine screws (Hobson's IMS04BTC037 range), 15 to 82mm long, which Hobson pairs with it.
• •You need a security Torx bit or key in that T size to fit them, and to take them out again.

Working out the screw length

The barrel goes into the parts from one side and the screw comes in from the other to meet it. Two things have to hold: the barrel length L must be no more than the total thickness of the parts, so both heads can clamp; and the screw must not run past the barrel's thread length TL, or it bottoms out before the joint is tight. Thread engaged = screw length less (thickness less L), and it can be at most TL. Hobson gives no minimum engagement or load rating, so where the fixing matters, follow the designer's specification.

Worked example (arithmetic on Hobson's dimensions): parts 40mm thick with an M8 x 30 barrel nut (TL 21.5mm). The screw has to cross 40 less 30, or 10mm, before it reaches the barrel, so the longest screw that can tighten is 10 + 21.5 = 31.5mm. An M8 x 30 screw engages 20mm of thread.

Hobson gives no hole sizes. Drill the barrel side to clear the barrel diameter S for the length of the barrel, and the screw side to clear the screw; try it in an offcut first.

304 stainless: where it suits

• •Hobson lists these barrel nuts in 304 stainless (A2). Hobson's corrosion guide for metal connectors accepts 304 or 316 stainless for exposed work in every zone it lists, including sea spray, except within 2m of a pool edge, where it calls for 316. For pool surrounds, the 316 countersunk pin Torx barrel nuts are on the barrel nuts page.
• •Hobson's stainless article notes that neither 304 nor 316 is made to sit in seawater, and that rust marks on stainless usually come from carbon steel contamination or the wrong grade for the site.
• •Stainless screw into a stainless barrel can gall (the threads seize). Hobson's galling guide suggests a slower installation speed, a thread lubricant containing molybdenum disulphide, or different stainless grades for the two parts.

How to fit a security barrel nut

1. Check the barrel length against the thickness of the parts and pick the screw length (above).
2. Drill through the parts: barrel diameter on the barrel side, screw clearance on the other.
3. Push the barrel nut in from one side and pass the screw through from the other.
4. Start the screw into the barrel by hand, then tighten both heads with pin Torx bits or keys of the right T size, at a steady, moderate speed. Stop when the heads are snug.

Security barrel nuts in Adelaide

Allmat supplies pin Torx barrel nuts, security screws, bits and keys to councils, park and playground installers, joiners and builders across Adelaide and South Australia. Add the barrel nuts to a quote with the screws and bits, and we will price the lot.

Questions