scope:

This specification covers the requirements for manufacture, coating, mechanical properties, microstructure, chemical composition, quality, quality plan and source approval and quality control. Recommended steel grades are given in Section A.0 - General Information.

Restricted Chemical Substances

All product supplied to the requirements of this specification must comply with the requirements of the MPAPS B-50 specification.

APPLICATION

This specification covers two types (Type A and Type B) of high strength U-Bolts used to fasten springs, fifth wheels, tow loops, and similar parts, where higher clamp load capacity is required. Both types of U-Bolts can be provided as either quenched and tempered (Q&T) products or as cold-drawn and stressrelieved (CDSR) products. The new Type B U-Bolt exhibits higher strength properties.

Type A

Type A is the traditional MPAPS F-1053 U-Bolt. It may be provided as either a Q&T or CDSR product. It provides high strength (equivalent to the obsolete SAE Grade 7) properties as indicated in Section 4.3. Type A U-bolts, CDSR, ¾" dia and smaller, will meet the mechanical property requirements of Grade 8.1 studs as shown in Table 1 for Type B material.

NOTE: For all existing Engineering drawings (and/or part numbers) that reference this specification without designating a material TYPE, Type A U-Bolt product shall be supplied, unless otherwise specified on the Engineering drawing as MPAPS F-1053 U-Bolt, Q&T, with SAE Grade 8.1 mechanical properties.

Type B

Type B is a new higher strength U-Bolt (having strength properties equivalent to SAE Grade 8.1) as indicated in Section 4.3. It may be provided as either a Q&T or CDSR product.

Restriction on Application of Type B

Application of the Type B material is restricted to the "round-top" series of U-Bolts, designated as STYLE 065 (See Eng. Dwg 453945C1). The Type B material shall not be applied to any of the "flattop" series of U-Bolts designated as either STYLE 050 (see Eng. Dwg 453872C1) or STYLE 060 (see Eng. Dwg 453892C1). The Type B material shall not be provided for any U-Bolt part whose Engineering drawing does not specify U-Bolt Type B. All new Engineering drawings for U-Bolts must specify a bolt Type as: U-Bolt Type A or U-Bolt Type B.

Preferred Manufacturing Process

Types A and B U-Bolts may be manufactured using either the Q&T or CDSR process. The CDSR process provides improved resistance to fatigue loading and is the preferred manufacturing process.