T-Slot Nut 20 Series M5 Hammer Nut for 20×20 Aluminium Extrusion

Where an M5 nut sits in the 20 series system

Twenty series is the light end of the T-slot family: a 20 x 20 mm envelope with a 6 mm slot, used for guards on small machines, sensor and camera brackets, display frames, light assembly benches and covers. Everything about the system is scaled down, and the fasteners are scaled with it. An M5 nut weighs about 2.5 g in steel and carries a fraction of what a 40 series M8 nut carries, which is the correct trade for a frame whose members are 20 mm square.

The consequence for the buyer is that the accessory range is smaller than it is in 40 series, and the fixings are less forgiving. There is no centre bore to fall back on in most 20 series sections, so the slot nut is not one option among several — it is the connection. The rest of the fastening elements and connecting elements range for 20 series is dimensioned around the same 6 mm groove, which is why a nut bought to the wrong groove cannot be made to work by choosing a different bracket.

Pre-install or post-install, and why it decides the build order

There are two ways to get a nut into a 6 mm slot and they are not interchangeable once the frame is assembled. The first is to slide it in from the open end of the extrusion before the end is capped. The second is to hold the nut with its long axis across the slot, drop the head through the 6 mm mouth, and rotate it a quarter turn so the head lies along the groove. The first uses the cheapest nut and the second uses a nut made for the job, and choosing the wrong one shows up late in the build.

On a 20 series frame this matters more than it does on a heavy frame, because the members are short and the frames are often closed on every side. A guard frame assembled and then fitted with a mesh panel has no open end left to slide a nut in from, so a panel clip added at that stage has to be a post-install fixing. Ordering the wrong type is not a small error on a light frame: it means either dismantling the corner or drilling a hole in a 20 mm member, and neither is what the drawing called for.

The two ways a small M5 fixing fails

A light fixing does not fail gradually, it fails at one of two places. The first is the thread: an M5 nut in a 10 mm body has a short column of engagement, and if the screw is over-tightened or reused, the thread in the nut shears and the screw turns freely. The second is the slot itself. The lips of a 6 mm slot are thin, and the load from the nut head is concentrated on two narrow strips; tighten far enough and the aluminium yields, the lips flare, and the nut no longer has anything to bear against. From that point the fixing looks tight but slides under load.

There is also a slow version of the second failure that has nothing to do with over-tightening. Aluminium creeps under a sustained load at quite modest stress, so a joint that is correct on day one can lose a little preload over months of vibration, and once the preload is gone the nut is free to walk along the slot. On a light frame this is rarely dangerous, but it is the reason a re-check of the fixings is part of routine maintenance on equipment that shakes.

• Thread stripped in the nut: screw reused many times, or a torque wrench set for M6 used on an M5 screw.
• Slot lip crushed or flared: nut tightened until the aluminium yielded, usually on the softer 6063 sections.
• Nut rotated in the slot: a screw longer than the groove depth bottomed out and pushed the nut off its seating.
• Corrosion staining at the joint: a stainless nut in an aluminium slot in a wet environment without a barrier between the two metals.

Material, and the small weight difference that is not small

The standard nut is carbon steel, zinc plated, and for indoor equipment that is the right choice: it is the cheapest, it has the hardest thread and it will outlast the frame. 304 stainless is specified where the frame is washed down, sited outdoors or exposed to condensate, because the zinc on a plated nut is the first thing to go. 316 is reserved for chloride or chemical exposure, where 304 alone will pit. Aluminium nuts exist mainly for two reasons: to remove the galvanic couple between the nut and the profile, and to save weight on a frame that is handled or moved.

The weight point is worth a number on this size. A steel M5 nut is about 2.5 g and an aluminium one is under 1 g, so on a display frame with two hundred fixings the difference is roughly 300 g. That is not a structural argument, but on a portable or suspended frame it is a real one. The cost of an aluminium nut is a weaker thread, so it belongs on light joints tightened by hand feel, not on a joint that will be torqued repeatedly.

Ordering, price and lead time

We supply the M5 20 series nut in carbon steel zinc plated and in 304 stainless, in both the slide-in and the quarter-turn post-install form, packed in bags of 500 or in bulk cartons. The minimum order is 5,000 pieces per material and type, and mixed orders across the two types are priced on the combined quantity. Unit price falls sharply with volume because these are cold-formed parts, so a 500,000 piece order is a fraction of the price of the minimum order.

Lead time is 10 to 18 days after deposit for zinc plated stock and 15 to 22 days for 304, which needs its own run. Trade terms are FOB, CIF or EXW, payment is T/T 30 % deposit with the balance before shipment, or an L/C at sight. OEM and ODM are both available: we can mark the head with your part number, supply the nut on a custom head width to suit a non-standard groove, or produce a special length for a deep bracket, and we will quote from a sample or a dimensioned sketch.

Frequently asked questions