Description of Tools (continued)

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Hand Drilling Hammers

Nomenclature

Head	The double face hammer head is made of heat-treated, high carbon steel.	Single jack
Striking faces	The two striking faces should have beveled edges and should be heat treated.
Handle	Wood handles are usually made of hickory. They should have a tight, knot-free grain that runs parallel to the wedge slot. Other handles are made of fiberglass, or are a forged extension of the head.	Engineer's hammer
Single jack	These are also called 'club' or hand drilling hammers. Handles are commonly 10 inches long, and heads weigh either 3 or 4 pounds. The short handle is uniquely suited to hand drilling because it resists breaking better than longer ones, and it facilitates accuracy by requiring the hand to be close to the head.
Engineer's hammer	These are also called long handle single jacks. They come with a 14-inch handle attached to a 3- or 4-pound head, and work well for the drilling technique we call modified double jacking.	Double jack
Double jack	These large driving sledges have 36-inch handles and 6- or 8-pound heads. Because their use requires considerable expertise from both the driller and holder, we recommend that you use single jacking or modified double jacking until safety and proficiency with the double jack can be assured.

Description of Tools continued...