A wheel moves because of the axle, and the wheel hub connects both parts to make the system fully functional. Your trailer’s wheel hubs are as important as the wheels themselves, and therefore requires the same maintenance. Failing to do so might cause difficulty in steering or result in a broken axle.
The wheel hub has studs that corresponds to the number of holes, or lug bolts of the wheel, which makes it possible for the hub to connect it to the axle. On either side of the wheel hubs are bearings, both inner and outer, which are basically cylindrical pieces packed with grease to reduce friction. It’s important, therefore, to keep the wheel hub adequately lubricated to avoid excessive heat due to friction, and this is where a grease cap, or a dust cap, comes in. It keeps the grease in and dust out, because dust and water can impede the performance of a wheel hub.
In replacing a wheel hub, count the number of studs or lug bolts on one wheel, which can be as many as four to five bolts per wheel. If the wheel has even-numbered studs, you can start measuring the distance between two opposite bolts. If the wheel has five studs, however, measure the distance between two opposite bolts (disregarding the bolt that will come in between) and multiply the measurement by 1.0515.