In top hammer rock drilling tools, an extension rod (also called an extension steel or extension drill rod) is a component used to extend the length of the drill string, allowing for deeper drilling without requiring a single, impractically long rod.

What is it Used For?

1. Depth Extension: When drilling deep holes, multiple extension rods are added between the drifter rod (connected to the drill) and the drill bit.

Each new rod extends the reach of the drill string progressively.

2. Energy & Flushing Transfer: Transmits percussive energy and rotation from the drill to the bit.

Allows compressed air/water to pass through for hole cleaning (like drifter rods).

3. Modular Drilling System: Enables flexibility—rods can be added or removed based on hole depth requirements.

Main thread sizes for drifter rods: R25, R28, R32, R38, T38, T45, T51 (male-male)

Main steel shape and sizes: round 32mm, 38mm, 45mm, 51mm(sometimes are hexangular steel)

Material: 23CrNi3Mo

Processing technology: Carburized

Main applications: Blast hole drilling (mining, quarrying).