Goliath's spear shaft was compared to what?

Answer: A weaver's beam

The shaft was like a weaver's beam and its iron point weighed six hundred shekels. A shield-bearer went before him.

“The shaft of his spear was like a weaver’s beam, and its iron point weighed six hundred shekels. In addition, his shield bearer went before him.”— 1 Samuel 17:7 (BSB)