Studs, Nuts, and Bolts

A.R. Thomson Group offers a full line of studs, nuts and bolting products. All of our industrial studs and nuts complement the bolted joint assembly and are manufactured in accordance to the latest editions of ASTM and ASME.

Quality

A.R. Thomson Group maintains an ISO 9001:2015 Quality Management System. Full traceability with heat codes and lot numbers ensures 100% compliance. Positive material identification, NACE, ASTM, and hardness certification are all available upon request.

Products & Materials

All Thread Studs: ASTM A193 Grade B7, B7M, B8, B8M, B16; ASTM A-320 Grade L7 and L7M
Heavy Hex Nuts: ASTM A194 Grade 2H, 2HM, 4, 7L, 7LM, 8 and 8M
Custom Coatings: Xylan, Teflon®, Cadmium, Zinc
Washers: ASTM F436 Hardened Steel Flat Washers, Stainless Steel and Belleville Washers
Specialty Fabricated and Machined Studs: Carbon Steel and Stainless Steel (specialty alloys available upon request)
Thread Lubricant: CANFLEX® Approved – Helps control friction and ensures uniform compression of the gasket in the bolted joint assembly

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Nuts

For each bolt/stud specification, there is an associated nut specification. Since both parts interact, it is important to refer to the nut standard as well. The ASTM standard for nuts related to the above for bolts and studs is:

1. 1. • ASTM A194/A194M – Specification for Carbon and Alloy Steel Nuts for Bolts for High Temperature or High Pressure Services, or Both. While this standard is indicated for high temperature services, it is also applied to low temperature services

The EN/ISO standards for nuts related to the above for bolts and studs are:

1. 1. • EN ISO 898-2 – Mechanical properties of fasteners made of carbon steel and alloy steel Nuts with specified property classes. Coarse thread and fine pitch thread
      • EN ISO 3506-2 – Mechanical properties of corrosion-resistant stainless steel fasteners Nuts

The tension in the fastener (and hence the compressive pressure on the gasket) is generated by tightening nuts along the threads of the bolt. The threads therefore play a major role in the clamping operation and care must be exercised to maintain their integrity. Threads will strip when the axial forces on the fastener exceed the shear strength of the threads. The main factors which determine stripping strength are:

1. 1. • the size of the fastener
      • the length of engagement of the threads
      • the strength of the materials from which the bolt/stud and nut are made

The threads on a larger bolt/stud are “longer” per turn and have thicker roots than the threads of a smaller bolt/stud. This means that the per-thread area which must be sheared to strip the threads is greater on a larger bolt/stud, which means greater stripping strength. Increasing the length of engagement between threads increases the cross-sectional area of the material which must be sheared to strip the threads.

Threads strip more readily when bolt/stud and nut materials are of the equal strength. For optimum safety, use a nut which has a specified proof load 20% greater than the ultimate strength of the bolts/studs. When done this way, the bolts/studs will break before the nut threads will strip. Remember, a break is easier to detect than a stripped thread!
Also note the effect of “galling”, which is the cold welding (partial or full) of one heavily loaded surface against another. It is encountered when the surfaces are brought together so intimately that molecular bonds form between mating parts, for example, between a nut and a bolt. This occurs when surfaces are highly loaded, when threads are a tight fit, when lubricants have migrated or dried out and when threads are damaged. This is compounded at high operating temperatures or when corrosion has occurred. It is difficult to eliminate galling, but the following may help:
• use coarse threads, rather than fine
• use the correct lubricant
• select materials for bolts/studs and nuts which in combination are resistant to galling, such as cold drawn 316 stainless steel on cold drawn 316 stainless steel, 400 steel nuts and 316 fasteners, etc.
Finished hex nuts are the most common type. Heavy hex nuts are used in high temperature and high pressure applications. This is the most common type of nut for flanged joints. Heavy hex nuts are slightly larger and thicker than finished hex nuts.

Material Identification on Nuts

A=Americas; B=Europe; C=Stainless Steel