[ArkyBeagle]

3/8 is half between 1/4 and 1/2. 5/16 is half between 4/8 ( 1/2 ) and 3/8.

[Turing_Machine]

And going the other way, 2 * 3/8 = 3/4, and 2 * 5/16 = 5/8, both of which are also standard sizes.