Tooth thickness nomenclature Gear

circular thickness 
length of arc between 2 sides of gear tooth, on specified datum circle.
transverse circular thickness 
circular thickness in transverse plane.
normal circular thickness 
circular thickness in normal plane. in helical gear may considered length of arc along normal helix.
axial thickness
in helical gears , worms, tooth thickness in axial cross section @ standard pitch diameter.
base circular thickness
in involute teeth, length of arc on base circle between 2 involute curves forming profile of tooth.
normal chordal thickness
length of chord subtends circular thickness arc in plane normal pitch helix. convenient measuring diameter may selected, not standard pitch diameter.
chordal addendum (chordal height) 
height top of tooth chord subtending circular thickness arc. convenient measuring diameter may selected, not standard pitch diameter.
profile shift 
displacement of basic rack datum line reference cylinder, made non-dimensional dividing normal module. used specify tooth thickness, 0 backlash.
rack shift 
displacement of tool datum line reference cylinder, made non-dimensional dividing normal module. used specify tooth thickness.
measurement on pins 
measurement of distance taken on pin positioned in tooth space , reference surface. reference surface may reference axis of gear, datum surface or either 1 or 2 pins positioned in tooth space or spaces opposite first. measurement used determine tooth thickness.
span measurement 
measurement of distance across several teeth in normal plane. long measuring device has parallel measuring surfaces contact on unmodified portion of involute, measurement wis along line tangent base cylinder. used determine tooth thickness.
modified addendum teeth 
teeth of engaging gears, 1 or both of have non-standard addendum.
full-depth teeth 
teeth in working depth equals 2.000 divided normal diametral pitch.
stub teeth 
teeth in working depth less 2.000 divided normal diametral pitch.
equal addendum teeth 
teeth in 2 engaging gears have equal addendums.
long , short-addendum teeth 
teeth in addendums of 2 engaging gears unequal.