Idealguides

Classifying Bolts / Machine Screws

Unified Thread Standard (The US standards for threads per inch)

Major diameter (inches)Threads per inch
Coarse (UNC)Fine (UNF)Extra fine (UNEF)
#0 = 0.0600   80  
#1 = 0.0730 64 72  
#2 = 0.0860 56 64  
#3 = 0.0990 48 56  
#4 = 0.1120 40 48  
#5 = 0.1250 40 44  
#6 = 0.1380 32 40  
#8 = 0.1640 32 36  
#10 = 0.1900 24 32  
#12 = 0.2160 24 28 32
1/4 20 28 32
5/16 18 24 32
3/8 16 24 32
7/16 14 20 28
1/2 13 20 28
9/16 12 18 24
5/8 11 18 24
3/4 10 16 20
7/8 9 14 20
1 8 14* 20

Bolt Types

TypePicture
Thread Cutting Bolt  
Carriage Bolt
Set Screws
Eye Bolt  
J-Bolt  
U-Bolt
Shoulder Bolt  
Elevator Bolt  
Sex Bolt  
Mating Screw  
Hanger Bolt  

Bolt Head Styles

NameAbbreviationProfileTop
Hex HH, HX, HHMB  
Washer Head WH    
Flat FH  
Pan PN  
Button BH  
Round RH  
Truss TH  
Oval OH, OV  

Bolt Materials

MaterialAbbreviationDistinguishing FeaturesPicture
Zinc Plated Z    
Stainless Steel SS Usually not magnetic  
Galvanized G Chalky dull appearance  
Chrome C Very shiny appearance  
Bronze B Golden / bronze color  

Hex Bolt Grades

Steel Hex Bolt Grades

Note, if the bolt is blank and doesn't have a manufactuer marking on this list. It's best to assume that it doesn't meet any specification. If it has a manufactuer marking that's on this list than it probably meets the grade 2 specifications.

Specification BodySpecificationGradeMarkingMartensitic SAE J429 1 No SAE J429 2 ASTM A307 A SAE J429 5 No ASTM A449 1 SAE J429 5.2 Yes ASTM A449 2 SAE J429 7 No SAE J429 8 No SAE J429 8.2 Unknown ASTM A354 BD No
Specification Grade Marking Martensitic Specification Body bolt
SAE 1 No place SAE J429 grade 1

Stainless Steel Hex Bolt Grades

AlloySpecification BodySpecificationMarking

303, 304, 304 L, 305, 384, XM1, 18-9LW, 302HQ, 303Se

ASTM F593C

Bolt Drive Styles

Drive TypeAbrevationPicture
Hex HH, HHMB
Square SQ
Phillips PH
Slotted, Straight Blade SL
Combination (Philips + Slotted)    
Hex Socket HEX
Torx TRX
One way  
Robertson ROB