Fasteners This work is licensed under the Creative

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Bolts • Most common on most machines (hex head bolts, and socket head bolts) • Made in standard sizes starting at ¼” and increasing by 1/16” up to 5/8” and in 1/8” steps up to 1” • Come in either coarse thread or fine, also right hand (most common) and left hand threads

Bolt Parts

Identification SAE (Standard) Metric

SAE Markings

SAE Nuts • Grade 2 -no marking or • Grade 5 - • Grade 8 -

Metric Markings

Left Hand Markings Some bolts and nuts have an “L” or “LH” to signify left hand threads as well as these

Why left hand threads? • There are many uses in industry for left hand threads • • • Left hand pedal on a bicycle Left hand grinding wheel on a bench grinder Lug nuts on some cars and trucks Cryogenic tanks Instances where a right hand thread would loosen

Other Markings • Bolts and nuts can have other markings from different manufacturers or different materials • Manufacturers sometimes put company logos, initials, or other identification on hardware • Stainless steel hardware also has different markings that identify the grade and hardness

Thread Sizes • For all SAE bolts there are 2 thread sizes • UNC-Unified National Coarse thread • 1/4 -20 UNC-less threads/inch • UNF-Unified National Fine thread • 1/4 -28 UNF-more threads/inch • For ISO metric bolts the mm/thread is greater for coarse thread and less for fine thread but there can be many different thread variations for the same size bolt

Bolt Sizes Classifications SAE • ¼-20 -UNC • ¼=diameter of bolt in inches • 20=number of threads/inch • UNC=national coarse thread Metric • M 12 x 1. 5 • M=metric screw thread • 12=diameter of bolt in mm • 1. 5=number of mm between threads

Common SAE Threads

Common Metric Threads

Measuring Threads • Thread pitch gaugeeasiest way • SAE and Metric take different gauges • SAE-threads/inch • Metric-mm/thread • Another simple way is to find a mating part

Identifying Bolts • Identify if the bolt is standard or metric by looking for markings of grade • If no markings you can measure thread diameter • Measure thread diameter to get the nominal bolt size • This measurement will be slightly smaller than the nominal bolt size • Measure threads to find out metric mm/thread or threads /inch • This can be done with a thread pitch gage or any mating part • Measure the length of the shank and threads to get overall length • Measure across the flats of the head (or the inside of a socket head) to find the wrench size • Again this dimension will be slightly smaller than a nominal size

Identifying Nuts • Identify if the nut is standard or metric by looking for marks on the top or the side of the nut • If none are visible, measure the wrench size • To get wrench size, measure across the flat surfaces • This dimension will be slightly smaller than a nominal size • To get the major thread diameter, measure the inside of the hole • The measurement that you get is the tap drill size • Take this measurement and search the chart for a size that it belongs to To measure thread pitch use a thread pitch gage or a mating part