Correction: Proper length for entrance reducer is 14 1/2"
Nothing goes to waste in a beekeepers workshop! Entrance reducers can be made from commonly destined for the wood pile. This one features two different entrance, one at 1" and another at 3" depending on your needs (or the bees for that matter).
One tip, is it can be useful to taper by the top and the back side
(relative to the picture). Sometimes you will find the reducer just does
not want to fit (moisture in wood equals expansion). This can alleviate
that problem. All it takes is a hand planer, even your hive tool or pocket knife can take off just a bit.
Just 1/16" to 1/8" can be just enough to create problem free entrance reducers. I just did the end for demonstration.