Albert Barnes Commentary 1 Samuel 17:7

"And the staff of his spear was like a weaver`s beam; and his spear`s head [weighed] six hundred shekels of iron: and his shield-bearer went before him." — 1 Samuel 17:7 (ASV)

Spear's head - literally, “the flame of his spear,” the metal part which flashed like a flame.

Six hundred shekels - that is, between seventeen and eighteen pounds avoirdupois.