Over time, even the sturdiest wood handles can split and crack. When this happens to garden forks and spades, it's a nuisance; with picks, axes, and sledgehammers, it's dangerous because the head can fly off in midswing. For safety, deeply cracked handles should be replaced.
For handles that are splintered but not deeply cracked, prevent further damage with hockey-stick tape, available at sporting-goods stores. Begin several inches beyond the splinter, and wrap the tape tightly around the handle, overlapping each layer by one-half to two-thirds the width of the tape. Repeat with a second layer of tape for heavyweight tools.