Go to your local hardware store and buy a caliper, they are not expensive and they can be handy for other projects. You can't just go by dimensions when buying components, you also have to size the reel seat to the reel foot on the reel, they are not all the same, for instance a 17 mm reel seat may fit your back bouncing blank, but your Shimano Tekota reel has to large a reel foot to fit the reel seat, it's to long and to wide. A 20 mm reel seat is the minimum size that will accept the longer and wider reel foot of the saltwater designed Tekota reels. Happens many times on salmon rods, people purchase a rod on sale one day and than get a good deal on a reel they like at a Sportsman's Show, or someplace, but you can't put the two together and go fishing.