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Square nuts are four-sided nuts as opposed to the more common hex (six-sided) nuts. The surface area on the flats is larger than hex nuts, which reduces wrench slippage. However, you cannot use hex drivers such as sockets and nut drivers. Machine screw square nuts are available in smaller sizes and also smaller in width and thickness than regular square nuts. Machine screw square nuts have flat tops and bottoms—the edges and corners are not chamfered (beveled). Regular square nuts have a flat bottom bearing surface and a crowned washer-faced top. Regular square nuts are often used with square bolts.
Threads are standard right-hand and Unified inch coarse series (UNC, Unified National Coarse) or Unified inch fine (UNF, Unified National Fine).
Square nut size refers to its nominal thread diameter. Typically, machine screw sizes range from about #2 to 1/2" and regular from 1/4" to 1 1/2". Sizes less than 1/4" appear as a number size (the larger the number the larger the size) while sizes that are 1/4" and larger are specified in inches, usually fractional rather than decimal.
Nut width, which is wrench size, and thickness vary with the size of the square nut. Table 1 lists width across flats and across corners, and thickness for machine square nuts; refer to Table 2 for dimensions of regular square nuts.
Steel, zinc plated, is a common material and finish.
Refer to ASME B18.6.3 for specifications relating to machine screw square nuts and ASME B18.2.2 for regular square nuts.
Machine Screw Square Nut Dimensions
Regular Square Nut Dimensions
|3/4||1 1/8||1 17/32||21/32|
|7/8||1 5/16||1 25/32||49/64|
|1||1 1/2||2 3/64||7/8|
|1 1/8||1 11/16||2 19/64||1|
|1 1/4||1 7/8||2 9/16||1 3/32|
|1 3/8||2 1/16||2 13/16||1 13/64|
|1 1/2||2 1/4||3 1/16||1 5/16|