Looks to me like a 108 is very similar to a 103 except :
The part below the bridge is smaller than the 103.
The 108 carts do not fit on the 103 because of this, the 103 atomizer pokes too far in to the 108 cart
A 103 cart will not work on a 108 atty because the 108 atty will not touch the 103's cart wick.