81-166S vs 81-166?

Thanks for reaching out to us. The given dimensions for these products is accurate. The housing style is similar but it is a little different between the two of them. 

You can try the 81-166S if you think you can get the 1-1/4" style to work in your door. Otherwise, you could always get the 81-166 and 81-266 wheel kit (sold separately). You can then install a new steel wheel on the 1-5/16" style.