Capacity is the rated load per axle. A tandem trailer with two 7,000 lb axles has a 14,000 lb axle rating. To size it: take the loaded trailer weight (trailer plus cargo), subtract the 10 to 15 percent carried by the tongue or pin, and divide the rest across your axles. Round up, never down.

Replacing an existing axle? Match the capacity on the old axle's tag, or match your spring axle's rating if you are converting to torsion. Each tier maps to a Dexter Torflex class (#10 through #13HD), so a like for like swap is straightforward.

Braked axles come with hydraulic disc brakes, the spec Hydrastar builds exclusively: stronger and more fade resistant than drums, with fewer parts to service. Idler hubs have no brakes at all and simply carry load, common as the second axle in a tandem or on light utility trailers.

Most states require brakes on trailer axles above a weight threshold (commonly 3,000 lb, it varies by state). When in doubt, brake every axle: stopping distance is the cheapest insurance on the road.

The bolt pattern is the lug count and the diameter of the circle the studs sit on: 5 on 4.5" means five studs on a 4.5 inch circle. It must match your wheels, so count the studs on your current wheel and measure the circle (for even counts, measure center to center across opposite studs). The code in parentheses is Hydrastar's order form notation.

Stud size is the thread diameter of the wheel studs. Bigger studs clamp harder and carry more load, which is why heavy axles require 5/8" studs and light axles run 1/2". The builder only offers sizes that pair with your pattern and capacity.

Hub face is the distance from the outside face of one hub (where the wheel bolts on) straight across to the outside face of the other hub. Outside bracket is the distance across the outside edges of the two mounting brackets on your frame. Hub face is always the larger number.

Measure with the tape level, on the old axle if you have one, or off the trailer frame for the brackets. The builder checks both numbers against the valid build range for your capacity as you type. Full walkthrough with photos: measurement guide. Still unsure? Call us and a tech will confirm them with you.

The torsion arm connects the axle tube to the hub, and its starting angle sets your ride height. An up angle puts the hub above the tube, so the frame sits lower: good for low decks and easy loading. A down angle puts the hub below the tube, raising the frame for more ground clearance. 0 degrees is in between.

Replacing an axle? Match the angle of the old one to keep the same deck height. The angles here match the diagram on the paper order form: 22.5 UP, 10 UP, 0, 10 DWN, 22.5 DWN, 35 DWN. Note that the arm rotates upward as it takes load, so a loaded trailer rides slightly lower than empty.

Bracket style: Single brackets are the standard mount. Double brackets (D) add a second plate for extra shear strength on hard working trailers. Heavy Duty (H) is required hardware on 8K and above.

Orientation: Standard Top Mount (Outboard) bolts to the bottom of the frame rail with the brackets outside, the most common setup. Reverse Side Mount (Inboard) tucks the brackets inside the rails for frames where outboard hardware will not fit. Match what your trailer already has unless you are changing the frame.

Side mount brackets installed: choose Yes to have the side mount hardware welded on at the factory, No if you are installing your own.

Tube profile: Straight Cambered is the standard tube with a slight built in arch so it sits flat under load. V Bend Cambered adds a shallow V to the tube for extra load leveling on wide or heavily loaded trailers. If you are not sure, Straight Cambered is the common spec.

Finish: Raw is bare steel, fine if you paint after install or run dry climates. Painted is the standard protective coat. Powder Coated is a baked on finish that takes gravel and road salt better than paint. Galvanized is hot dip zinc, the pick for boat trailers and salt exposure. Some finish and hardware combinations have build constraints; if yours does, the quote will flag it.

Fluid type: Grease packed hubs are the familiar standard, serviced with a grease gun. Oil bath hubs run the bearings in gear oil with a sight glass, run cooler on long highway miles, and are favored by fleets for service intervals. For occasional towing, grease is plenty.

Submitting sends your spec to Hydrastar as a quote request, no payment is taken and there is no checkout. Enter your name, email, and phone so we can reach you; add your company if you order on a business account. Hydrastar reviews the spec, then emails your price, confirmed lead time, and a single invoice for the full amount, usually within one business day. There is no deposit and no second invoice, payment is due in full before work starts. Quantity is how many identical axles you need; use the PO field if your shop runs purchase orders.