What is the difference between a 5A and 5B Drumstick?

I have recently had to convert over to using numbered sticks after using Zildjian Z4A stick for decades.
Zildjian has stopped making the stick for some reason.

I know the 5A is a much lighter stick and the 5B is a bit thicker.
Would the 5A feel like a toothpick or is the 5B a bit like a lincoln log in your hands?
Any info would be appreciated.

It can depend on the manufacturer. I have several 5A and 5B models and they vary from manufacturer to manufacturer. Mostly it is the shape of the neck and bead shape.

I have some 2Bs which aren't much different than 5Bs by another maker.

You will definitely find a 5B to feel beefier that a 5A. If the 5B was too much and a 5A too light you might try a 5B maple stick. Of course, the tips are not the same sting as a hickory. I use nylon tips so it's a moot point, and I have used maple for a couple decades now. The hickory 5Bs I sometimes use for pad work feel like telephone poles compared to maple.

There's no drum shops around where you can try some things out?

Send an email off to Zildjian and ask them what a close stick to the Z4A would be.

You will definately notice the difference between a 5A and a 5B.
About as much as you'd notice thd difference between a 7A and
a 5A.