Thought to mention to anyone looking for a wood block, Vaughan has mentioned he wants the lengthwise grain to run up and down the height of your mod for best strength. Sometimes sellers have blocks with dimensions that look like they would work, but the width (or height) along the grain is not tall enough. Example of this piece with the sellers dimensions of 3 7/8" x 2 3/4" x 2":
If you notice, the grain is running from left to right. That means you would actually flip this piece over on it's side. This changes the dimensions to 3 7/8"L x 2"W x 2 3/4H" (98.4mm x 50.8mm x 69.8mm) and what you need for a 18650 mod is 60mm L x40mm W x 80mm H. That makes this piece not tall enough by 10.2mm.
I initially saw this piece and immediately thought of
@emotionalstabilitysloth (sorry if I offend, sloth - it was intended as a compliment). Here are some other views of it (it is quite the beautiful, unique piece and is stabilized):
This bit makes me think of a sloth peeking through the wood in the knot on the right, little more than half-way down:
