What Is a QL Shank in DTH Drilling?

A QL shank is a splined connection on a DTH (Down-The-Hole) bit that transmits percussion energy from the hammer's piston directly into the bit body. The shank sits inside the hammer's drive chuck, secured by a retaining ring rather than a threaded connection — this lets the bit float freely for the piston strike while the splines transfer rotational torque.

DTH drilling is a percussion method where the hammer works at the bottom of the borehole, directly behind the bit, rather than at the surface. Because the hammer travels down the hole with the bit, shank geometry has to match precisely between bit and hammer chuck — a mismatch causes energy loss, accelerated wear, or chuck damage.

Shank compatibility is ultimately determined by the hammer, not the bit alone — it's the DTH hammer chuck's spline geometry that decides which shank standard fits. Confirming that before ordering replacement bits avoids the most common sourcing mistake: buying by nominal diameter without checking which shank standard the hammer chuck actually accepts.

QL shank sizes in current compatibility data run from QL40 up to QL200, with each number tied to a hammer size class and a matching recommended bit diameter range. This guide covers confirmed specifications across that range, including a gap in the lineup worth knowing about before you assume QL covers every diameter in between.

QL Shank Models — Bit Diameter, Air Pressure & Rotation Data

The table below lists confirmed QL shank specifications, drawn from MSD's own hammer/bit compatibility data.

Note: There is a gap in confirmed data between QL80's upper limit (254mm) and QL200's lower limit (457mm) — see the section below before assuming QL covers everything in between.

QL40 and QL50 — Smaller-Diameter Range

QL40 covers 110–135mm at 1.2–2.0 bar with a 30 Hz impact rate — the fastest in the QL lineup — and pairs with API 2 3/8" Reg pipe thread. QL50 steps up to 135–155mm at 1.3–2.3 bar and can also pair with 3 1/2" or 7/8" thread in addition to 2 3/8", giving it more rig flexibility than QL40.

QL60 and QL80 — Mid-Range Production Sizes

QL60 (155–203mm) and QL80 (195–254mm) move to 1.5–2.5 bar and 1.5–3.0 bar respectively, with impact rate dropping to 25 Hz and 22 Hz as bit diameter increases. Pipe thread steps up accordingly — 3 1/2" Reg for QL60, 4 1/2" Reg for QL80 — reflecting the added torque these sizes carry.

QL200 — The Largest Confirmed QL Size

QL200 jumps to 457–610mm, by far the largest confirmed bit diameter range under the QL name — nearly double QL80's upper limit. Air pressure steps up to 1.8–3.2 bar with 32–65 m³/min air consumption, but impact rate, rotation speed, and drill pipe thread are not specified in current data for this size. If you're speccing a QL200 application, confirm these three figures directly with the hammer manufacturer rather than assuming they scale linearly from QL80.

The QL80–QL200 Gap — What Covers 254mm to 457mm?

Here's something worth flagging before you assume the QL name covers every diameter between its smallest and largest confirmed models: there is no QL-named model in current data between QL80 (up to 254mm) and QL200 (from 457mm). That leaves roughly a 200mm-wide band — the size range that includes most large-diameter blast hole and foundation work — without a QL-specific entry.

This doesn't mean the diameter range can't be drilled — other shank standards fill it. DHD1120 and SD10/SD12 both cover portions of the 254–445mm band under their own model names. If your target hole diameter falls in this gap, the practical options are to select a hammer built around one of those other shank standards, or to check directly with the hammer manufacturer whether an unlisted QL model exists for that range — don't assume QL80 or QL200 specifications apply to sizes in between.

Shank Standards Are Not Interchangeable by Diameter Alone

QL, DHD, SD, COP, and MISSION are separate shank standards, each with its own spline geometry and hammer chuck design — matching nominal bit diameter alone is not enough to confirm compatibility. A QL60 bit will not seat correctly in a DHD- or SD-branded 6-inch hammer even though the bit diameter ranges overlap closely.

For a broader look at how shank standards compare across brands, see our DHD Shank guide and SD Shank guide. When ordering replacement bits, always confirm the shank standard stamped on the hammer's chuck housing rather than matching by diameter or model number alone.

Selecting the Right QL Shank Bit

Matching Compressor Output to QL Size

Air consumption scales with size — QL40 needs as little as 5 m³/min at 1.0 bar, while QL200 needs up to 65 m³/min. Before committing to a QL80 or QL200 bit, confirm your compressor's rated output against the air consumption figures above; underpowering a large QL shank reduces both rotation speed and flushing effectiveness before the bit itself shows wear.

Rock Formation and Button Selection

Button shape selection is independent of shank size but should match formation hardness — spherical buttons for highly abrasive hard rock, ballistic buttons for softer to medium-hard formations where penetration rate is the priority. For mining drilling in abrasive ore bodies, spherical buttons on QL60–QL200 sizes are the more common pairing; for water well drilling in smaller diameters, QL40–QL50 with ballistic buttons is more typical.

Drill Pipe Thread Considerations

Pipe thread steps up through the range — API 2 3/8" Reg for QL40, up through 3 1/2" and 4 1/2" Reg for QL60/QL80. QL200's thread specification isn't confirmed in current data, so check it directly rather than assuming it continues the same progression. Pair the bit with correctly rated DTH drill pipes to keep the full string consistent.

QL Shank Maintenance — What to Check Between Runs

Check the shank regularly for spline wear at the drive face, the surface that transmits rotational torque from the hammer chuck. Visible rounding at the spline edges, elongation in the retaining ring groove, or a noticeably looser fit against the chuck are the signs to catch before they cause a stuck bit or accelerated chuck wear. Because impact rate drops steadily from QL40's 30 Hz down to QL80's 22 Hz, larger sizes deliver more energy per blow for fewer cycles — worth factoring into how often you schedule inspections as you move up the size range.

Pair shank inspection with routine pneumatic DTH hammer chuck and piston checks, since a worn chuck accelerates shank wear on every bit that runs through it afterward.

Frequently Asked Questions

• Q: What bit diameter does QL80 cover, and what comes after it?
  A: QL80 covers 195–254mm. The next confirmed QL size is QL200, starting at 457mm — there's a gap in current data between the two. For diameters in between, check other shank standards like DHD or SD, which have models covering that range.

• Q: Does QL200 run at the same rotation speed as smaller QL sizes?
  A: Not confirmed. Rotation speed, impact rate, and drill pipe thread aren't specified in current data for QL200. Confirm these directly with the hammer manufacturer before ordering rather than assuming they follow the same pattern as QL40–QL80.

• Q: Can a QL60 bit fit a DHD or SD-branded 6-inch hammer?
  A: No. QL, DHD, and SD are separate shank standards with different spline and chuck geometry, even when bit diameter ranges overlap closely. Always confirm the shank standard stamped on the hammer's chuck housing before ordering.

• Q: What drill pipe thread does a QL50 bit need?
  A: QL50 can pair with API 2 3/8", 3 1/2", or 7/8" drill pipe thread, giving it more flexibility across different rig setups than QL40, which uses 2 3/8" only.

• Q: Why does impact rate drop as QL shank size increases?
  A: Larger QL shanks deliver more impact energy per blow, and hammer design trades impact frequency for that added energy. QL40 runs at 30 Hz versus QL80's 22 Hz — this is a normal design tradeoff related to piston mass, not a defect.

Technical content reviewed by MSD Engineering Team. | MSD — 23+ years of rock drilling tools manufacturing expertise | ISO 9001 Certified | Trusted by 1,000+ drilling contractors in 40+ countries