Mild Steel

SEMS Machine Screw

SEMS machine screws with a captive spring and flat washer already assembled under the head.

About the SEMS Machine Screw

SEMS machine screws have a spring washer and flat washer already fitted under the head, so electricians, appliance and switchboard builders and assembly lines can fix terminals, brackets and covers without handling loose washers. They are zinc plated mild steel pan head screws to JIS B 1188, with Phillips drive in M3 to M6 or Torx drive in M3 and M4, 6 to 30mm long, in packs of 200. Choose the drive, size and length above; the guide below covers what SEMS means, driver bits and where zinc plating suits.

Also called sems screws, screws with captive washers or washer assembly screws.

Features

Captive spring + flat washer, pre-assembled
Pan head, Phillips or Torx drive
Faster line assembly, no loose washers
Zinc-plated finish

Applications

Switchboards and electrical gear
Appliance and panel assembly
Production and line assembly

What is a SEMS screw?

Hobson explains SEMS as an abbreviation of asSEMblieS: a screw and washer assembly. These are metal thread (machine thread) pan head screws with a spring washer and a flat washer assembled under the head, which Hobson calls double washer assembly screws that save time and are easy to install. The washers are captive, so there are no loose washers to pick up, drop or forget.

Like any machine screw, a SEMS screw does not cut its own thread: it screws into a tapped hole, a nut, a rivet nut or another threaded insert. That makes them a common choice for assembling equipment, electrical panels, enclosures and appliances, and anywhere the same screw and washers go in over and over.

Hobson publishes no strength class, torque or anti-vibration rating for these screws: they are mild steel to JIS B 1188, and the documents we hold make no locking claim for the spring washer. Where a joint must not loosen under vibration, use the locking method the equipment designer specifies.

Phillips or Torx, and which bit

Phillips: M3, M4 and M5 take a Phillips #2 bit; M6 takes a Phillips #3.
Torx: M3 takes a T10 and M4 a T15. The Torx versions come in M3 and M4 only.
Both are pan heads: a raised, rounded head that sits on the surface, with the two washers under it.

SEMS screw sizes

Every SEMS screw we carry. Select a row to open that size and drive in the selector, then pick the length.

Zinc plated mild steel SEMS pan head screws with captive spring and flat washers, JIS B 1188. Thread is diameter x pitch (mm), metric coarse, fully threaded. Lengths in mm. Bit sizes from Hobson's Did You Know sheet. Pack is the minimum order quantity. Tap a number to show it in the selector above.

Thread	Drive	Bit	Lengths (mm)	Pack
Phillips
M3 x 0.5	Phillips	Phillips #2	6, 8, 10, 12	200
M4 x 0.7	Phillips	Phillips #2	8, 10, 12, 16, 20	200
M5 x 0.8	Phillips	Phillips #2	10, 12, 16, 20, 25	200
M6 x 1	Phillips	Phillips #3	10, 12, 16, 20, 25, 30	200
Torx
M3 x 0.5	Torx	T10	6, 8, 10, 12	200
M4 x 0.7	Torx	T15	8, 10, 12, 16, 20	200

Zinc plated: indoor and dry

Hobson rates zinc plating (5µm) as low corrosion resistance and recommends it for indoor and non-corrosive environments. Its corrosion guide for metal connectors accepts zinc plating as the minimum only for enclosed work in very low and low corrosion areas; anything sheltered or exposed to the weather needs galvanising or stainless.

SEMS screws are only available zinc plated. For outdoor, wet or coastal work, use 304 or 316 stainless machine screws with separate stainless washers from the machine screw page.

Fitting SEMS screws

Match the thread to the hole, nut or insert: an M5 SEMS screw goes into an M5 tapped hole, nut or rivet nut.
Choose a length that passes through the part and the two washers and still engages enough thread in the hole or nut.
Use the right bit (table above) so it does not cam out and damage the head or the zinc.
Tighten to the equipment maker's specification; Hobson publishes no tightening torque for these screws.

SEMS screws in Adelaide

Allmat supplies SEMS screws, machine screws, nuts, rivet nuts and driver bits to electricians, panel builders, fabricators and maintenance crews across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.

SEMS screws for assembly and panel work

SEMS machine screws, machine screws, nuts, rivet nuts and driver bits are available to order from Allmat for electricians, panel builders, fabricators, maintenance fitters and trade across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.

Send your list for a quote Call 1300 03 03 63

Goes with

Questions

What does SEMS mean on a screw?

Hobson explains it as an abbreviation of asSEMblieS: a screw supplied with its washers already assembled. Ours have a spring washer and a flat washer captive under a pan head.

What washers are on a SEMS screw?

A spring washer and a flat washer, held captive under the head so they cannot fall off.

What bit do I need for an M4 SEMS screw?

A Phillips #2 for the Phillips version or a T15 for the Torx version. M3 takes Phillips #2 or T10, M5 Phillips #2 and M6 Phillips #3.

Are SEMS screws stainless?

Not these: they are zinc plated mild steel. For stainless, use 304 or 316 machine screws with separate stainless washers.

Can I use SEMS screws outdoors?

Zinc plating is for indoor and non-corrosive environments in Hobson's finish guide, so not for outdoor, wet or coastal work. Use stainless machine screws and washers there.

How are SEMS screws sold?

In packs of 200, in every size and length.

Where can I buy SEMS screws in Adelaide?

Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.