An auger is one of the most versatile attachments you can put on a skid steer. Fence posts, deck footings, tree planting, sign poles — if you need a hole, an auger digs it faster and more consistently than any other method. But put the wrong auger on the wrong machine, or grab the wrong bit for the soil you are working in, and you will stall out, overheat hoses, or spin in place all day. This guide covers everything you need to match your auger to your machine and your job.
Standard Flow vs. High Flow Auger Drives
Your first decision is matching the drive to your machine's hydraulic output. Getting this wrong is the most common and most costly mistake contractors make when buying an auger.
- Standard flow (15-21 GPM): The Digga standard flow auger drive handles the majority of fencing, landscaping, and general post hole work. If your machine runs standard flow, this is your drive.
- High flow (25-40 GPM): The high flow auger drive gives you faster rotation speed, more torque, and the ability to run larger diameter bits in harder soils. If your machine has high flow capability, use it — you will see the difference on every job.
Do not put a high-flow drive on a standard-flow machine. It will underperform and can cause hydraulic overheating. Check your machine's rated GPM output in the spec sheet or owner's manual before buying.
Understanding GPM and Torque
These two specs determine what your auger can actually do in the ground, and most people only pay attention to one of them.
GPM (gallons per minute) controls rotation speed. Higher GPM means the bit spins faster, which increases how quickly you penetrate soft to medium soils. But speed without torque gets you nowhere in hard ground.
Torque is the pulling force that drives the bit through resistance. Hard soils, rocky clay, and frozen ground require high torque to advance. A high-GPM, low-torque drive will spin freely on top of hard soil without penetrating.
The matching logic is simple: check your machine's GPM, match it to the drive's rated range, then select a bit based on the torque required for your soil conditions. The sections below walk through bit selection by soil type.
Choosing the Right Auger Bit for Your Soil
Soft to Medium Soils — Topsoil, Loam, Clay, Sandy Soils
This covers most landscaping, fencing, and general construction work. Standard cutting teeth handle these conditions without any issues.
- General purpose auger bits — the go-to for most contractors. Handles topsoil, loam, and standard clay without issue.
- Light condition earth bits — optimized for softer soils where you want maximum penetration speed with minimal resistance.
Bit diameter: go 2-3 inches wider than your post or footing diameter to leave room for backfill or concrete. For a standard 4x4 fence post, a 6-8 inch bit is right. For Sonotube footings, run 10-12 inches.
Hard Soils and Mixed Rock — Hardpan, Rocky Clay, Gravel
When you are hitting compacted hardpan, dense gravel, or mixed rock, standard teeth will wear down fast and torque out. You need carbide-tipped teeth designed for abrasive conditions.
- Digga RC4 rock and earth combo bits — carbide-tipped teeth handle mixed rock, hardpan, and dense gravel. Slower rotation, higher torque, longer tooth life in abrasive conditions.
Using general purpose bits in rocky ground is one of the fastest ways to destroy teeth. If you are regularly working in mixed soil conditions, the RC4 is worth having in the truck.
Full Rock and Frozen Ground
This is beyond general purpose territory. Rock auger bits with full carbide tooth coverage are required. Expect slow progress, short strokes, and maximum torque demand from your machine. If you are hitting solid bedrock frequently, evaluate whether a different method makes more sense for that specific application.
Bit Sizing: Diameter and Depth
A common mistake is sizing the bit to the post exactly. You want 2-3 inches larger than the post or footing to leave working room:
- 4x4 fence post: 6-8 inch bit
- 6x6 post: 8-10 inch bit
- Deck footings (Sonotube): 10-12 inch bit
- Tree planting: match to root ball size, typically 18-24 inches
- Sign poles: match to post diameter plus 3 inches minimum
Standard bit lengths reach 3-4 feet, which handles the majority of fencing and landscaping jobs. If you need to go deeper, use extensions rather than trying to force a short bit further than it is designed to go.
When to Use Auger Extensions
Extensions add depth without requiring a different drive or a longer bit. The auger extension attaches between the drive and bit to increase your working depth. The TPE extension mount provides a clean, secure connection point for extended depth applications.
Practical guidelines for extensions:
- One extension in firm soil works well. You will notice slightly reduced torque transfer but nothing significant on standard depth jobs.
- Two extensions are possible in soft soil for deep post applications, but watch for bit deflection on long runs. The hole will drift if the soil has any variation.
- In hard or rocky soil, stick to one extension maximum. The torque loss and deflection risk increase significantly with depth in resistant material.
Common Mistakes and Troubleshooting
Auger spins but does not penetrate
You have the wrong bit for the soil conditions. General purpose teeth on hardpan or rock will spin on the surface without biting in. Switch to the RC4 combo bits and reduce your rotation speed to maximize torque.
Auger drive stalls under load
You are exceeding your machine's hydraulic capacity. This happens when the bit diameter is too large for your machine's GPM, or when soil conditions demand more torque than the drive can produce at your flow rate. Back off to a smaller diameter bit or step up to a high-flow drive if your machine supports it.
Hoses overheating
The drive's rated GPM range does not match your machine's output. A drive rated for 15-21 GPM on a machine pushing 30 GPM will overheat fast. Match the drive rating to your machine's actual output.
Hole walls collapsing
Wet or sandy soil will not hold a hole wall once the bit is withdrawn. Work quickly and pour concrete or set posts immediately after drilling. In extremely sandy conditions, a tube form in the hole before drilling can help hold the wall shape.
Frequently Asked Questions
What GPM do I need for a skid steer auger?
Standard flow auger drives typically operate between 10-21 GPM. High-flow drives need 20-40 GPM. Match the drive's rated range to your machine's actual hydraulic output — check your machine's spec sheet to confirm what it produces.
Can I use a high-flow auger drive on a standard-flow machine?
No. A high-flow drive on a standard-flow machine will underperform and risk overheating your hydraulic system. Buy the drive that matches your machine's flow rating.
How deep can a skid steer auger dig?
Standard bits reach 3-4 feet. With one extension you can reach 5-7 feet depending on the bit and extension length combination. Beyond that, deflection and torque loss make the hole unreliable for structural applications.
What is the difference between general purpose and rock bits?
General purpose bits have standard steel cutting teeth designed for soil, clay, and light gravel. Rock bits, like the RC4 combo, have carbide-tipped teeth for hardpan, dense gravel, and fractured rock. Running general purpose teeth in rocky ground burns through the teeth quickly and can stall your drive.
Should I rent or buy an auger?
If you are digging more than a few holes a year, buy. Rental rates for auger attachments run $150-300 per day. A quality skid steer auger drive pays for itself in 10-20 rental days. For contractors doing fencing, landscaping, or site prep regularly, it is not a close call.
Browse our full selection of skid steer augers including drives, bits, and extensions, or shop all post hole and drilling attachments.
