What is the difference between hex and heavy hex jam nuts?
A jam nut is a thin nut primarily used as a locking device, run up against a full-height nut that has been tightened into place to prevent that primary nut from loosening. Jam nuts are not used as structural parts and are commonly not manufactured to meet any specific nut specification since their primary function is to prevent the larger nut from backing off the threads. They are also occasionally used for leveling purposes.
Hex vs. Heavy Hex
The two styles available for a jam nut are hex and heavy hex patterns. The biggest difference between these two is sizing. The heavy hex pattern has a larger width across the flats and corners and is slightly thicker in comparison to the smaller hex pattern. Due to its larger pattern, the heavy hex jam nut is likely to have a higher proof load in comparison to its standard hex pattern counterpart. However, because these nuts are typically non-graded, there are not any strength comparisons available between the two.
Availability
Imported hex and heavy hex jam nuts are readily available in plain finish and hot-dip galvanized conditions. Imported stainless steel hex jam nuts are also available. These nuts are not graded in any way as mentioned above and do not come with any form of certification documents. For graded and/or domestic jam nut requirements they can be custom manufactured.
If you have a project that requires special jam nuts, give Portland Bolt a call. Our experts are standing by to assist with your custom needs.
Jam nuts say they are A563 grade A heavy hex, but MTR says proof load weaker than A563. Are jam nuts weaker than full sized nuts?
@Paul- The newest version of A563 added footnote G to Table 3 stating that the proof load for jam nuts is to be 60% of the full-size load. So yes, they are weaker than full-sized nuts.
I am looking for a clarification related to jam nuts. Hope you can help me.
Instead of a jam nut can we use a regular hex nut to prevent the primary hex nut from loosening?
What are the advantages and disadvantages if we use a regular hex nut in place of a jam nut?
Thanks & regards.
@JV- Regular hex nuts are commonly used in place of jam nuts due to their ease of availability and lower (usually) price. The disadvantage is that regular nuts are a bit larger, so if you are tight on space, they may not fit properly.