C.E. Smith Square Trailer U-Bolts: Inside Sizes & Threads
Replacing a square U-bolt on a boat trailer? These C.E. Smith fasteners secure suitable brackets and accessories to trailer frames, but the inside opening and thread size vary by manufacturer number. Compare the frame cross-section and the bracket's mounting holes before choosing the fastener.
Three measurements determine the starting point
Inside widthMeasure the clear opening between the U-bolt legs. Three parts in this chart have a 3⅛-inch inside width; galvanized 15283GA is slightly narrower at 3¹⁄₁₆ inches.
Inside lengthMeasure the available length from the bend toward the tips. Check the trailer frame, mounting plate, washers and required thread engagement together.
Thread size15252A and 15253A are 7/16-14; 15274A and 15283GA are 1/2-13. Use the correct mounting holes and matching nuts.
C.E. Smith square U-bolt dimensions
The zinc-plated models use a silver finish; 15283GA uses a galvanized-steel finish. C.E. Smith supplies matching nuts and washers with these U-bolts. Confirm the exact listing and application before installation.
| MPN | Inside width | Inside leg length | Thread | Finish |
|---|---|---|---|---|
| 15252A | 3⅛ in | 3 in | 7/16-14 | Zinc-plated |
| 15253A | 3⅛ in | 4 in | 7/16-14 | Zinc-plated |
| 15274A | 3⅛ in | 4¼ in | 1/2-13 | Zinc-plated |
| 15283GA | 3¹⁄₁₆ in | 3¹³⁄₁₆ in | 1/2-13 | Galvanized steel |
Inside dimensions matter: The opening between the legs is not the bolt's outside width, and the listed inside length is not a guarantee of sufficient thread engagement after adding a mounting bracket and washers. Verify the entire assembly against the trailer and accessory manufacturer's requirements.
Measure before fitting the replacement
- Measure the trailer frame. Check width and height at the actual mounting position, accounting for coating, welds and any obstruction.
- Check the bracket holes. A 7/16-inch threaded leg and a 1/2-inch threaded leg need different clearances. The same inside width does not make the bolt interchangeable.
- Check length through the stack. Add frame and mounting-bracket thickness to determine whether the bolt has sufficient usable threaded length once nuts and washers are installed.
- Match the coating and hardware. Distinguish zinc-plated models from galvanized 15283GA, and check the exact supplied nuts and washers.
- Install to the equipment instructions. Use the correct grade, tightening procedure and corrosion precautions for the trailer and mounted accessory. Do not reuse damaged or excessively corroded fasteners.
Shop exact square trailer U-bolts
Compare the four exact-MPN products below. NewRVParts orders ship from supplier warehouses; the parts are not available for warehouse viewing or pickup.
C.E. Smith 15283GA
Inside: 3¹⁄₁₆ in wide × 3¹³⁄₁₆ in long
1/2-13 threads · Galvanized steel
View exact U-boltRelated trailer support hardware
These fasteners are used with appropriate mounting brackets, but fit must be checked by the exact frame and bracket specification. For other trailer components, see the boat-trailer bunk support brackets and bunk carpet roll sizes guides.
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