OAL vs Working Length: Why the Difference Matters
The most common length-related mistake in SDS Plus bit procurement is treating the overall length (OAL) as the usable drilling depth. It is not. Every SDS Plus bit has three distinct length zones, and only one of them drills.
The Three Length Zones
Overall Length (OAL) — also called total length — is the measurement from the carbide tip to the very end of the shank. This is the number most prominently listed in catalogs and on packaging.
Working Length (WL) — also called usable length or flute length — is the measurement from the carbide tip to where the flutes end. This is the only part of the bit that can cut. When the flutes disappear into the chuck, drilling stops. Working length is the number that actually determines whether a bit will reach the required depth.
Shank Length — the unfluted cylindrical section at the end of the bit, including the SDS Plus groove engagement zone. On standard SDS Plus bits, this section is approximately 60–70mm. It is consumed entirely by the rotary hammer chuck and never contacts the workpiece.
The relationship is simple:
Working Length ≈ Overall Length − 65mm (for standard SDS Plus bits)
A 160mm OAL bit has approximately 95–100mm of working length. A contractor who needs to drill a 120mm-deep anchor hole and orders "160mm bits" will find that the bit bottoms out in the chuck before reaching full depth — because the actual usable length is only 100mm.
Usable Drilling Depth vs Working Length
There is a further deduction beyond working length: the practical drilling depth is slightly less than the WL because pulverised concrete dust accumulates at the bottom of the hole during drilling. Approximately 10–15mm of the hole depth is occupied by loose cuttings at any given moment. For accurate depth calculation:
Minimum WL required = required hole depth + 15mm clearance
For installations through overlay materials — tile, screed, insulation, or timber framing — add those thicknesses too:
Minimum WL = embedment depth + overlay thickness + 15mm
This formula is the starting point for every length selection decision in this guide.
Standard SDS Plus Lengths and Their Applications
SDS Plus bits are available in a defined set of standard lengths. While custom lengths exist, the following OAL values represent the stock lengths carried by most distributors and manufacturers worldwide. The working lengths shown are approximate averages — actual WL varies by ±5mm depending on manufacturer shank design.
| OAL | Approx. WL | Usable Drilling Depth | Typical Applications |
|---|---|---|---|
| 110 mm | ~45 mm | ~30 mm | Plasterboard, lightweight partition blocks, shallow plug anchors (M6 in soft masonry) |
| 160 mm | ~100 mm | ~85 mm | Standard residential anchor work, M6–M8 anchors in concrete, brick walls, general installation |
| 210 mm | ~150 mm | ~135 mm | M8–M12 anchors, drilling through tile + concrete, MEP through concrete blocks, cavity wall penetration |
| 260 mm | ~200 mm | ~185 mm | M16–M20 anchors, structural fixings through thick screed, insulated concrete sandwich panels |
| 310 mm | ~250 mm | ~235 mm | M20–M24 structural anchors, floor-slab penetrations, deep conduit sleeves, through-wall pipe penetrations |
| 460 mm | ~400 mm | ~385 mm | Full wall penetrations (200–350mm walls), deep foundation anchor bolts, MEP conduit entry through thick structure |
| 600 mm+ | ~540 mm+ | ~525 mm+ | Heavy structural walls, floor-to-ceiling penetrations, industrial slab drilling — typically 12mm+ diameter only |
The 160mm Bit: Why It Is the Default Stock Item
The 160mm OAL (100mm WL) is the most widely stocked SDS Plus length for one reason: it covers the majority of standard construction anchor installations. Fischer, Hilti, and Rawlplug chemical anchor systems for M6 through M10 bolts typically specify embedment depths of 50–90mm in normal concrete. Add 15mm clearance and a 160mm bit handles them all.
For distributors sourcing a first range, 160mm should make up the largest portion of the SKU inventory across all diameters. 210mm is the second most important — it covers the M12 and above anchor market, plus the very common scenario of drilling through a tile or screed layer into the structural concrete beneath.
The 110mm Bit: The Misunderstood Short Bit
The 110mm OAL bit is frequently misunderstood as a "starter" or budget bit. It is not — it is a specialist length. With only ~45mm of working length (usable depth ~30mm), it cannot reach the embedment depth of any standard expansion anchor in concrete. Its actual use cases are: wall plugs in hollow brick or light block walls, where the depth is shallow and the material is soft; and as a stub bit for drilling through hard tile to expose the substrate before switching to a longer bit. Most contractors do not need 110mm bits in their regular rotation.
Anchor Embedment Depth to Bit Length: Reference Table
The table below maps common anchor systems to the minimum working length required, then to the appropriate standard OAL bit. Embedment depths shown are for normal concrete (C20/25); some anchor systems specify greater depths in lower-strength concrete — always check the anchor manufacturer's technical data sheet.
| Anchor / Application | Hole Ø | Embedment Depth | Min. WL Needed | Recommended Bit OAL |
|---|---|---|---|---|
| M6 expansion anchor (nylon plug) | 6 mm | 25–35 mm | 50 mm | 160 mm |
| M8 chemical anchor (normal concrete) | 10 mm | 80 mm | 95 mm | 160 mm |
| M10 expansion anchor (concrete) | 12 mm | 75–90 mm | 105 mm | 210 mm |
| M10 through tile + concrete (10mm tile) | 12 mm | 90 mm + 10 mm tile | 115 mm | 210 mm |
| M12 chemical anchor (concrete) | 14 mm | 110 mm | 125 mm | 210 mm |
| M16 expansion anchor (structural) | 18 mm | 125–140 mm | 155 mm | 260 mm |
| M20 chemical anchor (concrete) | 20 mm | 170 mm | 185 mm | 260 mm |
| M24 structural chemical anchor | 24 mm | 200–220 mm | 235 mm | 310 mm |
| Through-wall penetration (200mm wall) | varies | 200 mm full penetration | 215 mm | 310 mm |
| Through-wall penetration (350mm wall) | varies | 350 mm full penetration | 365 mm | 460 mm |
Embedment depths shown are indicative for standard concrete (C20/25). Always verify against the anchor system's technical approval documentation (ETA or ICC-ES report), as depths vary by anchor type, substrate strength, and loading conditions.
The Overlay Problem: Tile, Screed, and Insulation
One of the most common length underspecification mistakes occurs when drilling through a composite substrate — a tile layer on screed on concrete, or an insulated render system on masonry. The required anchor embedment is measured from the surface of the structural substrate, not from the visible surface. The overlay adds to the required working length but contributes nothing to structural holding capacity.
A common European bathroom anchor installation: 10mm ceramic tile + 50mm cement screed + concrete substrate. An M10 anchor requires 90mm embedment into concrete. The bit must pass through 10 + 50 = 60mm of non-structural material before the embedment even begins. Minimum WL required: 90 + 60 + 15 = 165mm. A 210mm OAL bit (150mm WL) fails — the usable depth is only 135mm. A 260mm OAL bit (200mm WL) is the correct specification.
This calculation is frequently missed at the point-of-sale because the overlay thicknesses are not visible on the surface. Distributors who teach their customers this calculation differentiate themselves from competitors who simply stock bits by length.
Diameter vs Length: Aspect Ratio Constraints
Not every diameter is available in every length. The limiting factor is the aspect ratio — the ratio of total length to diameter. A bit that is disproportionately long relative to its diameter will flex under the rotary hammer's lateral impact forces, causing the bit to wander off-axis, enlarge the hole beyond tolerance, and eventually fatigue-fracture at the flute root.
The practical limits for SDS Plus are:
| Diameter | Max Practical OAL | Notes |
|---|---|---|
| 5–6 mm | 160 mm | Extreme slenderness at 160mm; 210mm exists but prone to snapping under lateral load. Use only in soft masonry with care. |
| 8 mm | 310 mm (460 mm marginal) | 310mm is the reliable limit in normal use. 460mm 8mm bits exist but require experienced operators and straight-line drilling discipline. |
| 10 mm | 460 mm | Full range reliably available. 600mm+ exists in specialist deep-drilling configurations. |
| 12–16 mm | 600 mm+ | Full range available. At these diameters, longer bits are actually more stable due to increased body mass. 1000mm+ used in industrial applications. |
| 18–26 mm | 1000 mm+ | No practical length limit at these diameters within the SDS Plus system. Energy class becomes the limiting factor before aspect ratio does. |
Why Small-Diameter Long Bits Fail
When a 6mm SDS Plus bit at 210mm OAL is subjected to a 1.5J impact, the bit deflects laterally at the unsupported mid-span before the carbide tip can react. This deflection is partly elastic (the bit springs back) and partly plastic (it accumulates a permanent bend). The fatigue crack initiates at the first flute root below the chuck — the highest stress concentration point. The bit does not warn before it snaps. This is not a quality defect in the bit; it is a physics consequence of specifying the wrong aspect ratio for the energy level.
For deep, small-diameter holes (e.g., 6mm × 150mm depth), the correct technique is not a longer bit — it is a stepped approach: drill to 100mm with a 160mm bit, then attach an extension rod if required, or switch to a rotary-only mode for the final depth in soft material.
What to Stock: Length Range by Customer Type
A well-structured SDS Plus length range is not a uniform spread across all lengths. Demand follows an 80/20 distribution: most sales concentrate in two or three lengths, with the remaining lengths serving specialist applications. The correct split depends entirely on who the end customers are.
Residential and Light Commercial Installation
The dominant work type is anchor installation for brackets, conduit clips, partition frames, radiators, and kitchen cabinets. Substrate is typically concrete, lightweight block, or old solid brick. Anchor systems are M6–M12.
- 160mm: 60% of inventory. Covers the vast majority of M6–M10 anchors. Should be available in every diameter from 6mm to 16mm.
- 210mm: 30% of inventory. Covers M10–M12, tile-on-concrete scenarios, and cavity walls. Diameter range 8–16mm.
- 310mm: 10% of inventory. Deep anchors, through-wall cable runs. Diameter range 10–20mm.
- 460mm and 110mm: occasional specialty orders, not regular stock.
Commercial and Structural Construction
Work shifts to heavier anchor systems (M16–M24), thick reinforced concrete slabs, and wall penetrations for MEP services. Substrate is denser, depths are greater.
- 210mm: 30% of inventory. Still the most common for M12–M16 work.
- 310mm: 40% of inventory. The professional workhorse at this level. Covers M20–M24 anchors and most through-wall work.
- 460mm: 20% of inventory. Through-wall penetrations, deep structural anchors.
- 160mm: 10% of inventory. Light fixing work that still exists on commercial sites.
Industrial and Infrastructure
Specialist requirements — heavy foundation anchor bolts, utility penetrations through thick slab and walls, precast concrete connections. Here 460mm and 600mm+ become volume items, and the diameter range skews toward 16–26mm. Stocking decisions at this level should be driven by project-specific specifications rather than general distribution logic.
Quick-Reference Stocking Table
| OAL | WL | Residential / Light | Commercial / Structural | Industrial |
|---|---|---|---|---|
| 110 mm | ~45 mm | Occasional | — | — |
| 160 mm | ~100 mm | Primary (60%) | Secondary (10%) | — |
| 210 mm | ~150 mm | Secondary (30%) | Primary (30%) | Secondary |
| 310 mm | ~250 mm | Occasional (10%) | Primary (40%) | Secondary |
| 460 mm | ~400 mm | — | Secondary (20%) | Primary |
| 600 mm+ | ~540 mm+ | — | — | Primary (project-specific) |
For diameter selection guidance — which diameter range to stock for a given rotary hammer energy class — see the SDS Plus Energy Class to Diameter Matching Guide. For anchor hole diameter and embedment depth specifications by anchor type, see the Anchor Bolt Drill Size Chart.
Related Procurement Programs
If you are sourcing this product line for a distributor, importer, or private-label channel, these OEM and wholesale programs cover the procurement questions buyers usually ask next.
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