Rubber Bobbin Mounts: Hanging Loads, Snapped Studs and Oil Rot

A generator box hung off rubber bobbins, a stud snapped at the nut, or mounts gone soft and squat under a leaking engine: small bobbin mounts tend to fail for a handful of avoidable reasons.

Here is how to load them, fix them and choose the right ends. PartsForMachines stocks 735 rubber bobbin mounts made by AV Industrial Products, in metric threads from M3 to M20.

Can Rubber Bobbin Mounts Take a Hanging Load?

Not in pure tension: bobbins are made to work in shear, compression or a mix of the two. AV Industrial Products says plainly that, like all bobbins, its female-female range should not be put into tension.

So turn the bracket round. Angle or L-brackets under the box let the unit sit on the mounts, in compression, or bolt to their side, so they work in shear. A 5045FF10-60 female-female bobbin (M10, rated 86 kg) bolts neatly under such a bracket. A loop of chain or a catch plate will hold the unit if a mount ever lets go.

Why Do Bobbin Mount Studs Snap, and What Should Replace Them?

When a stud snaps or seizes, the answer is a new mount, because the threaded metalwork is bonded into the rubber. Keep the nuts tight, and recheck them after the first hours of running.

For separate bolts or studding, use property class 8.8: it has roughly twice the tensile strength of class 4.6.

An M8 thread written with no pitch is the standard coarse thread, 1.25 mm; a fine thread is written with its pitch, so check the old one. Check the stud length too: the 4035MM23-60 male-male bobbin has M8 x 23 mm studs, which must clear the bracket, washer and nut.

Do Oil and Diesel Ruin Rubber Mounts, and Why Do They Sag?

Yes: soft, swollen or greasy rubber under a leak is the sign. Oil and diesel attack rubber over time, natural rubber swells in oil, and heat speeds up the ageing. Fix the leak first, then shield the mount from drips.

Sag is partly normal. Rubber under constant load slowly creeps and takes a set, so a machine can settle a little after fitting. Check its level after bedding in. Where oil, fuel or heat cannot be avoided, ask our team about an oil-resistant or high-temperature rubber, which can be made to order for many sizes.

Male-Male, Male-Female or Female-Female: Which Bobbin Suits My Fixing?

Choose by what your frame and base already have. Male-male suits clear holes on both sides, with nuts; male-female suits one clear hole and one tapped face; female-female takes a set screw from each side.

The end type can change the rating, even on the same body. A 40 x 40 mm, 60 Shore bobbin carries 57 kg as the 4040FF08-60 and 55 kg as the 4040MF20-60 male-female bobbin. A 30 x 20 mm, 70 Shore body, though, is rated 53 kg as a male-female and 40 kg as a female-female. Thread size does not set the load either: our M8 female-female bobbins run from 10.4 kg to 120 kg per mount. Match the rating, then the thread.

What Should I Check Before I Order?

• the weight of the unit and how many mounts will share it
• the load direction: sitting on or beside the mounts, never hanging in pure tension
• thread size and stud length against bracket thickness, washer and nut
• the ends you need: male-male, male-female or female-female
• any oil, fuel or heat near the mount

Browse the rubber bobbin mount range, or contact the PartsForMachines team by WhatsApp, telephone or email with the weight, the thread and a photo of the old mount.

Product options, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

My machine wobbles on new bobbins when I push it. Is that normal?

Some movement is normal, because the rubber is meant to flex: the 4035MM23-60 deflects 3.1 mm at its 56 kg rated load. If the machine rocks freely or the rubber bottoms out, compare the weight with the mounts’ ratings.

Are female-female bobbins weaker than male-male ones?

Sometimes, but not always. On a 40 x 20 mm, 45 Shore body the female-female is rated 32 kg against 41 kg for the male-male; on a 50 x 30 mm, 60 Shore body the female-female is rated higher. Check the exact mount’s rating.

Can I replace just the stud on a bobbin mount?

No. The stud is part of the metalwork bonded to the rubber, so it cannot be swapped on its own. Fit a new mount, and replace the others in the set if they show the same wear.

The rubber is pulling away from the metal. Can I keep using it?

No, replace it. The bond between rubber and metal carries the load, so once it starts to part the mount can let go. Before fitting the new one, check for oil on the rubber or a mount working in tension.

The nut has seized on a rusty stud. What now?

Cut or split the nut rather than forcing it and twisting the mount. Then fit a new mount with fresh nuts and washers.

Do you have bobbins with imperial threads, such as 1/4-28 UNF?

Our bobbins are metric, from M3 to M20. Measure the old mount’s diameter, height and thread, then send the figures and a photo to our team so we can suggest the nearest metric fit.

Is it a problem if my mounts are rated for a lighter machine?

Yes, it can be. Each mount should be rated for the share of weight it carries, and the same-size body can differ a lot: the 2530FF08-45 is rated 10.4 kg and the 2530FF08-70 30.4 kg. Match the rating, not just the size.

What is a waisted bobbin, and when would I use one?

It is narrower in the middle than at the ends. The maker says the waisted shape spreads stress through the rubber for controlled deflection. The WMM1380-HT60 waisted bobbin has M8 studs and a 30 kg rating.

How often should I check bobbin mounts after fitting?

Check nut tightness and the machine’s level once it has run for a few weeks, as new rubber settles slightly under load. After that, look at them at each routine service for cracks, swelling or oil.