The backset is the distance from the forend to the centre of the spindle hole.
2 1/2 Inch
Body - 65mm with 44mm backset
Not bolt through
3 Inch
Body - 78.5mm with 57mm backset
Bolt through @ 38mm centres
4 Inch
Body - 102.5mm with 82mm backset
Bolt through @ 38mm centres
Latch includes strike plate and screws.
Item shown 3 Inch Polished Brass
Reversing the latch bolt
Hold the latch with 'this way up' facing you Remove the loose face plate Twist the brass latch bolt Replace the loose face plate 
