Thin jam nuts clamp against regular nuts to remove tightening force from fastened objects. Obviously, the supported weight of an object is anchored as intended, but the nuts don’t lock fully against its surface. Instead, the “jamming” nut tightens against a second hex nut to create an off-surface clamping force. It all begins with a vacant bolt, though, until two female pieces clamp against each other.

Describing Basic Geometry

Jam nuts are thinner than regular hex nuts. They employ the same diameter and internal pitch measurements, but, when viewed from the side, the profile of the jamming nut is thinner than its companion. Basically, it only needs to be large enough to clamp to the primary female fastener piece, so its thickness need only be wide enough to assure complementary locking action is accomplished.

Uses of Jam Nuts

Primarily, this is a type of two-piece locknut. It’s plainly adjustable, for both nuts can be screwed freely along the thread of the bolt. Once the optimal location is found, the thinner variant is positioned, at which point its regular companion is threaded tightly against its face. This process is sometimes referred to as “double-nutting,” although the “jamming” descriptor is a tad more expressive. If this locknut designation does describe a primary usage area, then a secondary purpose likely exists. One use that commonly employs this adjustable locking format comes quickly to mind. Imagine a bolt without a head. Perhaps the head is concealed or hidden in an enclosure. Regardless of the condition of the bolt head, the fastener needs to be tightened. Torque can be applied by “double-locking” the nuts and using a wrench to rotate the bolt rod.

Double-Locking Applications

There’s some fastening scenarios where plain locknuts don’t fit the bill. This could be a delicate plastic housing or a vibration-prone setting. If the plastic housing is subjected to the full torque required of the work, then it could crack. A series of regular nuts and an equal amount of jam nuts pair up to remove strain from the housing. The fragile object is properly supported, but no stress is directed at the plastic. In addition to this hypothetical application, double-locked fasteners promote finite adjustability, so rubber dampeners won’t be overly compressed when a vibration heavy application crops up.

They may be thin, but jam nuts are the best solution when adjustability is required from a set of locknuts. Just remember to evenly torque each pairing so that every face drives uniformly into its companion.

Get in touch

TCI Fasteners – Topcope
13 Slater Parade, Keilor East VIC 3033 Australia

Telephone: (03) 9336 0155