FlatA countersunk head with a flat top.Abbreviated FH
OvalA countersunk head with a rounded top.Abbreviated OH or OV
PanA slightly rounded head with short vertical sides.Abbreviated PN
TrussAn extra wide head with a rounded top.
RoundA domed head.Abbreviated RH
HexA hexagonal Head.Abbreviated HH or HX
Hex WasherA hex head with builtin washer.
Slotted Hex WasherA hex head with built in washer and a slot.
SlottedA slot in the head.Abbreviated SL
CombinationA combination of slotted and Phillips drives.Abbreviated Combo
Socket, Hex or AllenA hexagonal hole for use with an Allen wrench.
One WayInstalls with a normal slotted driver but can not be removed without special tools.
HexA six sided nut. Also referred to as a finished hex nut.
Nylon Insert LockA nut with a nylon insertto prevent backing off.Also referred to as a Nylock
JamA hex nut with a reduced height.
Nylon Insert Jam LockA nylock nut with a reduced height.
WingA nut with 'wings' for hand tightening.
CapA nut with a domed top over the end of the fastener.
FlangeA nut with a built in washer like flange.
TeeA nut designed to be driven into wood to create a threaded hole.
SquareA four sided nut.
Prevailing torque lockA non-reversible lock nut used for high temperature applications
K-Lock or KepA nut with an attached free-spinning external tooth lockwasher.
FlatA flat washer used todistribute load. Available in SAE, USS, and other patterns.
FenderAn oversize flat washer used to further distribute load especially on soft materials.
FinishingA washer used to obtain a 'finished' look. Usually used with oval head screws.
Split LockThe most common style of washer used to prevent nuts and bolts from backing out.
External Tooth LockA washer with external 'teeth' Used to prevent nuts and bolts from backing out.
Internal Tooth LockA washer with internal 'teeth' Used to prevent nuts and bolts from backing out.
SquareA square shaped washer.