I am repairing an old Brule (WIS) brand fiberglass musky rod. The damaged tip top was removed. The existing blank tip is somewhere between a size10 and 12. Customer wants a SIC tip top installed. I can't find a SIC in size 11. size 12 is way too sloppy. Size 10 doesn't come close to being large enough. Customer would prefer I don't cut back the blank. Do I "sand" the fiberglass until the 10 fits? Or do I cut the blank back? Remember, this is a musky rod.
Thanks,
Buzz

Neither. Never sand the tip area - this is just asking for trouble. And don't cut the rod - no need to alter it if you don't have to.

If you need to move up to the next larger tip top tube size, use some thread underneath to take up the space. If you normally add a thread trim at the base of the top tube, just use this wrap as an extension and carry it onto the area where the top will reside. When you get past the area where the rear of the tube will reach, begin to spiral the thread so any adhesive can reach the blank. Remember that you have several sizes of thread to choose from so a good fit can usually be easily accomplished.

I have seen SIC tops with an 11 tube but it seems that the ring sizes are rather large in those models. Hopefully one of the sponsors will contact you if they have a top that will fill your present need.

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I totaly agree with tom. If the tip top is a little sloppy shim with thread.
Never cut back on a blank uless it is to remove fractures