I've given it my best shot, and still do not have it clear in my head the differences between 16 and 17 casting seats. All I can find is that the 17 is usually longer, and the ID (bore for the blank?) is usually larger. The bore at the rear of both are the same size? Thanks in advance-I know this group can clear it up.

[alpsforecast.com]

You'll see that the ID of the 17mm seat is larger, which means that the barrel is also larger in OD. The 17mm seat is a bit longer. In regard to the back of the seat where it meets the rear grip, the OD is the same on 16, 17, and 18mm seats.

Thanks, Joe, that's what I thought, but was not sure. So what is in your hand is essentially the same on both. I see my using a 17 only if a 16 won't fit the blank.

I believe that if you check the diameter of the reel seat at the location of the reel - I think that you will find that the 17mm seat is larger and thus fits many hands much better.

Double check to be sure.

Take care

16 and 17 seats are different sizes both inside and outside but it's mainly dictated by the threaded barrel. A 16 seat will accept all hoods of like size, as will a 17. With the ACSM, for example, you have 12 different ID's (to match the blank), but only two actual sizes (16 and 17) based on the size of the threaded barrel.