A pump wrench, also sold as a water pump pliers or slip-joint pliers, is the tool people reach for when a nut or fitting is too big or too awkward for a spanner. Getting the right one comes down to a few practical factors.

Sizing the jaw

Pump wrenches are usually described by overall length, and the length roughly determines the maximum jaw opening. A 250 mm tool covers most plumbing and pump maintenance. A 300 mm or larger tool gives more leverage for seized fittings, but will not fit into tight housings.

Material and hardening

Look for chrome-vanadium steel with induction-hardened teeth. Soft jaws round off quickly and start slipping exactly when you apply real force. A hardened jaw holds its bite for years of regular use.

Self-locking or simple slip joint

• Slip-joint designs are adjusted by hand and are more compact.
• Self-locking designs grip harder as you pull, which reduces the force you need and is ideal for round or smooth pipe.

Where they earn their keep

Typical uses include loosening pump bodies, holding pipe unions, gripping round shafts, and freeing corroded fittings. On chrome-plated or polished surfaces, protect the finish with a cloth or use a tool with smooth jaws.

Choose the size for the space you actually work in, not just for the biggest fitting you might meet.