Threaded stems are often the ideal way to fasten casters for both practical and aesthetic reasons. But as you will see from this case study, when casters hang on by a thread, there are implications to consider.
One of our customers that manufactures equipment for the food service industry needed casters for their stainless steel carts. The casters attach to 1” tubing so there was no room for a top plate. In addition, the customer wanted the aesthetic effect of having the caster tuck nicely under the cart. Their solution was to order casters with a ½” threaded stem. So far, so good.
The carts would each carry about 1400lbs. of product so the customer ordered casters rated at 350 lbs. For one of our technical sales reps immediately that immediately sent off warning bells. He called the customer and urged him to order casters rated at a minimum of 500lbs. The customer was perturbed. Why would they need casters that provided that much additional capacity
This is where the sales rep’s knowledge and expertise came into play. He explained that most often maintenance staff are installing threaded casters, they don’t tighten the thread right to the raceway. That leaves a portion of the thread exposed. The carts are used in rugged industrial environments and frequently come in contact with some kind of impediment – divots, bumps and debris. When the cart hits something, the kingpin takes the impact and the exposed thread bends. The caster is toast.
Our rep explained that the way to protect the caster is to assume that its capacity is 30% less than the rating. That way when it inevitably encounters an obstruction, it will withstand the impact. That means that a 500 lb. caster with a threaded stem shouldn’t be counted on to accommodate more than 350 lbs. – which is why he suggested the 500lb. caster in the first place.
There’s no question that the higher capacity casters cost more but when you figure in the increased longevity and the decreased maintenance costs, there’s no question they are a smart investment.
As threaded casters become more popular on store fixtures and food grade equipment, engineers and those who spec the components would be wise to heed our advice and make sure that their equipment isn’t hanging by a thread.