SX 1845 A - Sixpence - Narrow date

The 8 & 4 are close together. 

The 5 has a large gap to the ribbon tie

9.5 teeth from 1 to centre of 5 

 SX 1845 B - Sixpence - Medium date

The 8 is evenly spaced from the 4

The 5 has a medium gap to the ribbon

10 teeth from 1 to centre of 5

 SX 1845 C - Sixpence - wide date

The 8 is evenly spaced from the 4.

The 5 is much closer to the ribbon

11 or 12 teeth from 1 to centre of 5