From here on out as the second picture shows a stock, a classic IE 1300, then a current 4 hole version on the right. All IE inputs now utilize four holes instead of two on the bottom of the shaft. Picture three is the exception the 727 / first gen 24 spline shaft has no holes. The third pic is measuring a IE 1300 23 spline shaft. The forth is of the 35 spline Fat shaft.