Trailer Adjuster Bolt Assembly

What a trailer adjuster bolt assembly is

Hobson lists this part in its high tensile range as a trailer adjuster bolt assembly (code KBS88GQM120030). What Hobson states about it: hot dip galvanised, class 8.8, HEC (Hobson's manufacturing mark), M12 x 1.75 thread, 30mm long and fully threaded, with a note that thread length can vary on older batches. It is sold as an assembly in packs of 100, and Hobson's product picture shows a hex head bolt with a hex nut.

Hobson publishes no data sheet, drawing, parts list or fitting instructions for it, and does not say which adjuster, on which make of trailer, it was made for. So we treat it as a replacement part: match it against the bolt you are replacing and the trailer or axle maker's parts list before you order, and ask us if you are unsure.

Trailer bolts are a safety job

Hobson publishes no load rating, capacity or tightening torque for this assembly. Bolts in a trailer's brakes, suspension, axle or coupling must be the parts the trailer or axle maker specifies, fitted to their instructions and torque; if this assembly is not the part named in that spec, use the maker's part. If you are building or modifying a trailer, the bolts are part of the design and need the designer's or engineer's specification.

Class 8.8 tells you the bolt material: Hobson's bolt technical data chart describes class 8.8 as medium carbon steel, quenched and tempered, with 8.8 marked on the head. That is a property of the steel, not a rating for this assembly on your trailer.

Size and specification

One size. Select the row to open it in the selector.

Checking it matches the bolt on your trailer

• •Thread: M12 with a 1.75mm pitch. Check it against the old bolt and nut; an imperial or fine thread nut will not fit it.
• •Length: 30mm. Compare it with the bolt you are taking out, measured the same way.
• •Thread form: this bolt is threaded all the way to the head. If the original has a plain shank, it is a different part; check with the trailer or axle maker before swapping it.
• •Class: the original should be marked 8.8 on the head. If it is marked 10.9 or higher, this 8.8 bolt is a lower class and is not a replacement: use the maker's part. Never replace a bolt with a lower class one.
• •Nuts and washers: keep the nut and washer arrangement the maker specifies. Our nyloc nuts and flat washers are on their own pages if the maker's spec calls for them.

Hot dip galvanised finish

Hobson's finish comparison gives hot dip galvanising about 50 microns of zinc with high corrosion resistance, and recommends it for long term outdoor use, which is where a trailer lives. Hobson's corrosion guide also lists stainless steel or hot dip galvanising for fixings exposed to the weather.

Do not worry if the galvanising looks dull. Hobson explains that newer galvanising comes out a matt grey rather than lustrous, with the same physical properties, and quotes the Galvanizers Association of Australia: brightness has no effect on performance, and the coating mass sets how long it lasts.

Trailer adjuster bolts in Adelaide

Allmat supplies trailer adjuster bolt assemblies, galvanised high tensile bolts, nuts, washers and trailer safety kits to trailer builders, mechanics, farmers and trade across Adelaide and South Australia. Add the bolts to a quote with the rest of your trailer parts and we will price the lot.

Questions