four-foot-long 4-by-4 in his hand' - what is it?

' Seeking to wreak vengeance, with a four-foot-long 4-by-4 in his hand, and righteousness in his heart, the highly-trained soldier, now the county's sheriff, and his deputy, realizes it's time to bust some heads with a very hard piece of wood.'
from Plot Summary for Walking Tall (IMDb)

A 4 by 4 is a piece of finished lumber whose cross-section is roughly 4 inches by four inches. (Or was before it was milled -- it's a little less once sanded.) It can be any length -- in this case four feet long. It would be used as a building material. Or to whack some sense into someone.

The pieces of lumber sticking upright out of the concrete in this photo are 4 by 4's:

http://www.sehgal.net/ObsConstruction/011026-1139-23.jpg

Thank you, Uriel. It helps.

BTW, recently I asked another question relating the IMDb's material, nobody's answered me yet. Let me ask it again:
<There are two confusing examples of preposition usage. Both - from IMDb site (the Internet Movie Database):
1. 'She has two children BY Tim Robbins...'

The 'by' in this context seems odd to me. And BTW, is it possible to use the same 'by' talking about Tim Robbins? 'He has two children BY Susan Sarandon'? Sounds strange...>

>> 1. 'She has two children BY Tim Robbins...' <<

It's an idiom plain and simple. X(female) has a child by Z(male). It's a fairly common expression.

Thank you, Q. A preposition 'By' in this context is a bit odd for me yet .

It's mainly used to denote parentage, in both animals and people. You can be slightly more coy and say "she has two children WITH Tim Robbins" but this also implies that she and Tim are still together, and isn't definitive about Tim being the actual biological father.

However, by saying that you have children BY someone, you are explicitly saying that they are the other half of the DNA team --- understand? Thus you will hear people say things like "She has two kids by her first husband, and one by her second" or "I had my mare bred by a registered stallion."

I may be wrong, but I think BY is more often used to indicate who did the fathering -- often FROM is used with mothers -- "He has kids from two different women". But I don't think that's a hard and fast rule -- I think you'll hear both BY and FROM used interchangeably with each sex.