Donaldson air cleaners are generally found on Freightliner, Kenworth, and Peterbilt trucks. The top cap, which is removed to change the filter, is held on by four bolts.
Nelson air cleaners are normally only found on Freightliner trucks. They are easy to distinguish from other brands because they do not have a stainless steel screen around the cap.
Premium Donaldson air cleaners feature a twist-off cap that, when removed, reveals four bolts underneath.
Vortox air cleaners are usually only seen on Kenworth and Peterbilt trucks. The top cap, which is removed to change the filter, is secured by a single long bolt that sticks up through the middle of the air cleaner.