I really don't buy file handles .. I turn em
There are two measurements that you need to know. One if the tang length and the second is the width of the tang half way up the tang. The width determines the diameter of the hole needed to insert the tang so that it does not split the handle when it is inserted. The length of the tang determines the depth of the hole in the handle.
To ease installation heat up the tang so that the metal is hot but not cherry read. Put the handle on the tang and tap it gently on the tang to seat it.
To determine which size of handle you need, check out the diameter of the hole in the handles to figure out the corresponding number size.