Flange & SEMS Bolts

What sems bolts are for, and which bolt does what

Hobson explains that SEMS is short for asSEMblieS: a screw and washer assembly. The washers are captive, fitted under the head before you buy them, so they cannot drop off on the way into the hole and every bolt goes in with its washer. That is why they are used where the same bolt goes in hundreds of times: Hobson lists the automotive, electrical and telecommunications industries, interior and quarter panels, aftermarket accessories and auto electricians, and says the flat washer sems bolt is common on manufacturing assembly lines, where the labour saved is worth more than the cost of the fastener.

• •Sems bolt (hex head, spring and flat washer): a class 8.8 bolt with a spring washer and a flat washer captive under the head, so nothing drops off during assembly. Hobson lists them for the automotive, electrical and telecommunications industries, interior and quarter panels, aftermarket accessories and auto electricians. M8 hex head, 16 to 50mm.
• •Sems hex bolt with a flat washer (M10 x 25, class 8.8 to AS 1110.1, zinc plated, fully threaded): one large outside diameter flat washer captive under a standard hex head, which spreads the bearing pressure and helps prevent damage to the part being fastened. Hobson lists it for any bolting job where a washer is needed. Hobson notes a test certificate or report is available for this code: ask us if you need it.
• •Sems hex Phillips bolt: the same idea with a hex head that also takes a Phillips driver, in M5 (12 to 25mm) and M6 (16 to 40mm).
• •Serrated flange hex bolt (DIN 6921, class 10.9, fine thread): the head has a built-in round flange that acts as a washer, with serrations under it; Hobson's sheet for its D-Lok serrated flange bolts describes such serrations as locking and clamping the connection (it publishes no sheet for these DIN 6921 bolts). Common on machinery, vehicles and frames where a fine thread high tensile bolt is specified. Ours are M14 x 1.5 and M16 x 1.5, 40 to 70mm, zinc yellow passivate. More flanged hex bolts (class 8.8, 10.9 and 12.9, coarse and fine, with and without serrations) are on the hex bolt page.
• •Cable tray bolt (M10 x 22): a smooth head so it does not damage cable sheathing, flat sides on the neck that stop it turning in the hole in the tray or ladder, and a square neck that fits the cable tray nut's counterbore. Hobson lists it for fixing splice plates, brackets and other accessories into cable trays and ladders, with its matching cable tray nut.
• •Stepped plow bolt (Grade 9, 5/8 UNC x 2-3/4 inch): a raised head with a stepped square neck, plain finish, for securing the cutting edges of earthmoving blades. The full plow bolt range is on its own page.

Sizes we carry

Every bolt in this range, by type. Select a row to open the first length of that type in the selector.

Sems bolt dimensions

From Hobson's Did You Know sheets. Use the hex size to pick a socket and the washer diameter to check the bearing face fits. For the M10 flat washer sems bolt, Hobson's spanner selection chart gives 16mm for an M10 hex bolt to AS 1110 (a DIN 933 M10 takes 17mm, so do not reach for a 17mm).

Cable tray bolt dimensions and nut

Hobson's Did You Know sheets give the M10 x 22 cable tray bolt a head height of 3.8 to 4.2mm, a thread length of 12.0 to 12.5mm and 16.8 to 17.0mm across flats (per Hobson's sheet). Use it with the matching M10 cable tray nut in the same finish (hot dip galvanised or zinc plated), on our serrated flange nut page.

Hot dip galvanised for cable tray outdoors, in plant rooms with moisture or anywhere the tray is hot dip galvanised; zinc plated for dry indoor runs. Hobson's zinc whisker article explains that whiskers grow from electroplated zinc and that none has been found on its hot dip galvanised range, which matters in data centres and other rooms full of electronics.

Finishes

• •Zinc yellow passivate (flange and sems bolts): about 5 microns of zinc with a yellow conversion layer, low corrosion resistance; Hobson recommends it for low-corrosion environments or temporary fixing.
• •Zinc plated (cable tray bolt and the M10 flat washer sems bolt): about 5 microns, low corrosion resistance, for indoor and non-corrosive environments such as machinery, panels and assemblies kept indoors.
• •Hot dip galvanised (cable tray bolt): about 50 microns, high corrosion resistance, for long term outdoor use. Hobson's corrosion guide lists hot dip galvanising or stainless for exposed fixings.
• •Plain (plow bolt): no coating, lightly oiled to stop rust in the packet.

Fitting tips

• •Flange bolts: the flange takes the place of a separate washer under the head.
• •Fine thread: the M14 x 1.5 and M16 x 1.5 flange bolts need fine thread nuts of the same pitch; standard coarse M14 and M16 nuts will not fit. M14 x 1.5 and M16 x 1.5 hex nuts (including class 10), nyloc nuts and lock nuts are on their own pages; match the nut class to what your drawing specifies.
• •Sems bolts: the washers are already captive under the head, so no separate washer is needed on that side. If your drawing calls for a washer under the nut, add a flat washer there. The M10 flat washer sems bolt takes an M10 x 1.5 nut or tapped hole and a 16mm spanner.
• •Cable tray bolts: fit the bolt with the smooth head on the cable side, so the cable sheathing runs against the smooth head, and tighten the cable tray nut on the other side.
• •Plow bolts: the square neck stops the bolt turning in the cutting edge while the nut is tightened. 5/8 UNC plow nuts are on the plow nut page.

Sems and flange bolts in Adelaide

Allmat supplies sems bolts, flange bolts, cable tray bolts, plow bolts and their nuts to auto electricians, manufacturers, fitters, electrical contractors, earthmoving workshops and trade across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.

Questions