Hey, Robin. The best way to determine what size spline you need is to measure the diameter of the handle's hole. That should tell you precisely what size is necessary.
Another great way to determine the handle is to identify the operator. Once you figure out what operator you have, you can just select one of the related handles we have on our site.
We have an Anderson wood Bow window from the second half of the 1970s. As the sill is quite distressed I'm installing a new sill the is about 1/4" thick. The existing cranks won't clear so I'm looking for T handles. My existing handles have set screws. How should I measure the diameter, on the outside of the splines or in the "shallows" between the splines? I can do it either way with my calipers.
thanks,
Max
Hello, Max. You want to measure the diameter of the hole, not the inner diameter of the teeth. The image below should give you a better idea of what I mean.
If you have an Andersen brand operator, then odds are the spline is 3/8".