Jam nuts are low-profile nuts that are half as tall as a standard hex nut. It's often used as a type of locknut where it is jammed up against a
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1/4 - Nuts - Fasteners - The Home Depot
1/4 - Nuts - Fasteners - The Home Depot
Stainless Steel 304 Nylon Insert Lock Nut,3/8-16, 1/4-20, 5/16-18, 50 PK
Nylon-Inserted Lock Nut Pack Chrome 1/4-20 UNC - Custom Chrome Europe
Set screw UNC 1/4-20 stainless steel (similar DIN 916)
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Aluminum Jam Nut - 1/2-20 Right Hand Threads - Pack of 4 - Reliable Welding & Speed On-Line Store
1/4-20 Track Nut, 6 Pack – Outdoor New England