Biothene Class A Miniature Driving Harness.  Complete Set. 
Bridle Measures 30" at the largest and 26" at the smallest tip to tip over the poll. (remember your bit (not included) will add some length due to the rings) The saddle measures 54" at the largest and 44" at the smallest around the inside.  
      There is plenty of room to make the saddle larger or smaller as needed and a few inches on each side to make the bridle larger or smaller if needed.  
 
The easiest way to know is If this will fit is using a bale string,  measure corner of the mouth to other corner over the poll and then right behind the withers, Then measure the string and compare the measurements above.