​The Long Cross Pennies of Henry III 

5a1

5b1

5d1/2/3

There are five sub-classes to differentiate:  5a1, 5b1, 5d1, 5d2, & 5d3

We need to look at the style of the letters X and R, and additionally bust style to differentiate between the 5d sub-classes.

5a1 : X2 R2

5b1:  X4 R1

5d1:  X5 R3 - Crude bust      Note that 5d coins have a characteristically different bust appearance, and unusual reverse spellings.

5d2:  X5 R3 - More realistic bust

5d3: X5 R3  - Neater bust, and distinctive sharp crown ends rather than half fleurs.

Some examples of X/R lettering: 

Coins with Sceptre - Class 5 with half fleur crown ends

All half-fleur coins are scarce or rare....