What type of nuts should I specify on leaf chain anchor bolts?
There’s no one size fits all when it comes to leaf chain anchor bolt nuts. The loads, vibrations and temperatures experienced during operation all impact performance – and some types of nuts are much more durable and easier to adjust than others. Here we break down some of the advantages and disadvantages of each type, depending on application.
As the leaf chain on off-highway equipment, such as forklift trucks, telehandlers and piling machines, wears over time, the nuts on the thread of the chain anchor bolts (clevis) need to be adjusted to maintain the correct tension. Different types of equipment experience varying levels of vibration according to their application, so the correct choice of nut can be key to lasting safe operation.
One full nut and one half nut
Leaf chain is traditionally fitted to a chain anchor bolt with two nuts – one full nut and one half nut. This method has been used for hundreds of years – you’ll see it on lots of vintage machinery – as it achieves a locking effect which prevents the nuts from becoming loose. It is also infinitely resealable, adjustable and reduces the risk of thread stripping as there is more surface area in contact with the thread.
Single nylon-insert lock nuts
These days, the use of a single nylon-insert lock nut (also known as a nyloc nut or elastic stop nut) is becoming increasingly common. Nylon-insert lock nuts feature a nylon collar that increases friction on the screw thread as the insert deforms over the thread as it is tightened. In a manufacturing context, these kinds of nuts offer fast and repeatable installation and can cost less than two classic nuts. Modern, high-quality nylon nuts can even be reused several times, although we still always recommend using fresh nuts, especially for critical fastener connections. Because nylon-insert lock nuts are not easy to adjust, however, we do not recommend them at all for high frequency lifting applications where frequent adjustments are required.
Self-locking nuts (also known as prevailing torque nuts or stiff nuts) are very resistant to vibration and, because they are all metal, they can be used in elevated temperatures and are not affected by oil. Their locking action is created by the distortion of their uppermost threads – they have a self-contained feature that creates interference between the threads of the leaf chain anchor bolt and the nut. Self-locking nuts even work when not fully tightened but it is important to check their strength as they are not available in all grades.
Castle nuts and slotted nuts
An option where the nuts are seated close to the end of the leaf chain anchor bolt is to use castle nuts or slotted nuts. These types of leaf chain anchor bolt nuts feature a pre-drilled hole where a split pin (cotter pin) can be inserted to secure the fixing and prevent movement. They can be fiddly to fit, however, and do not allow much adjustment.
Where vibration and loosening are a major concern
If your equipment is subject to a lot of vibration and loosening nuts are an issue, you might consider fitting wedge lock washers under the nut. These comprise a pair of washers with steps that, when tightened, lock against each other and are easy to regularly adjust if you need to. If you are looking for a more permanent fix, a thread locker can help. A thread locker is a type of semi-solid adhesive that sets to a solid plastic when placed between the two threads. However, this needs to be reapplied each time you want to adjust the position of the nuts.
At the end of the thread on many leaf chain anchor bolts it is common to find a hole for a split pin. Split pins do not normally take any load but are there just in case the nuts work loose. They can add to assembly time for new machinery builds and many of our new designs do not have them or use a spring clip, which is faster to fit.
For more information on nuts, we recommend visiting the TR Fastenings website. TR Fastenings highlights products and grades that should easily be available and has lots of useful technical specifications and CAD models that you can download.