Flex-Hone Grit Selection & Usage Guide
How to choose the right series, grit and abrasive — and how to use a Flex-Hone correctly
How to Select the Right Flex-Hone
Measure Your Bore Diameter
Use a bore gauge or inside micrometer to accurately measure the cylinder bore diameter. Flex-Hone tools are sized to fit specific diameter ranges — selecting a tool slightly larger than the bore gives the correct working tension.
Measure at multiple points and depths to account for wear, taper, or out-of-round.
Choose the Correct Series
BC Series — 4mm to 76mm (3")
Brake cylinders, valve guides, boiler tubes, small hydraulics
GB Series — 83mm to 117mm (3¼"–4⅝")
Standard automotive engine cylinders, hydraulic cylinders
GBD Series — 76mm to 203mm (3"–8")
Heavy duty — large automotive, diesel and marine cylinders
GBD Large Cored — 216mm to 457mm (8½"–18")
Industrial, marine and oil/gas bores; larger sizes by special order
Select Grit Size
Grit selection depends on material type, current bore condition, and the seals or rings being used.
| Grit | Grade | Best For |
|---|---|---|
| 120 grit | Coarse | Heavily glazed bores, aggressive deburring, rough stock removal |
| 180 grit | Medium | General engine reconditioning, most cylinder applications |
| 240 grit | Medium fine | Automotive cylinders, hydraulic cylinders, general finishing |
| 320 grit | Fine | Precision hydraulic and pneumatic cylinders |
| 400 grit | Extra fine | Critical sealing surfaces, high-precision bores |
Note: Flex-Hone grit ratings are not comparable to abrasive paper. A 180 grit Flex-Hone produces a far finer surface finish than 180 grit sandpaper. 180 and 240 grit cover ~99% of general applications.
Standard Flex-Hone Sizes & Grit Range
The standard Flex-Hone range uses silicon carbide (SC) abrasive and covers diameters from 4mm to 475mm (18"). Aluminium oxide (AO) abrasive is also available in a range of diameters suited to small tube up to 100mm for engine cylinders.
The main grit sizes are 180 grit (medium) and 240 grit (medium fine). Other grits available are 120 (coarse), 320 (fine), and 400 (extra fine). Finish can also be varied by lubricant weight — grease produces a finer finish than oil.
Abrasive types available: Silicon Carbide (SC) — cast iron, steel, general use. Aluminium Oxide (AO) — aluminium, brass, non-ferrous. Diamond — ceramics and carbide. Boron Carbide — hardened steel and titanium. Custom grit sizes from 20 to 800 grit and diameters up to 900mm (36") by factory special order.
Operating Instructions
- 1The Flex-Hone can be used in a variety of rotating spindles from CNC equipment to a portable hand drill. Do not use air tools or high-speed drill motors.
- 2Secure the tool in a collet, chuck or similar holding device. Ensure the connection is firm — the tool must not wobble.
- 3Coat the tool and bore liberally with lubricant. Use 10–30 weight cutting oil or Flex-Hone Oil. For hydraulic brake cylinders only, use hydraulic brake fluid. Never use kerosene or solvents.
- 4Start the tool rotating before entry into the bore. Maintain rotation throughout — do not stop rotating while the tool is inside the bore.
- 5Refer to the RPM & Surface Finish guide for recommended RPM by diameter. Use 60–120 strokes per minute. Hone for approximately 20–45 seconds per cylinder.
- 6After honing, immediately clean the bore with warm or hot water and detergent using a stiff brush to remove all abrasive residue. Dry and oil the bore immediately to prevent rust.
Important: Do not attempt to clean honed bores with kerosene or petroleum-based solvents — they embed fine abrasive particles into the bore surface. Hot water and detergent is the correct method.
Frequently Asked Questions
What lubricant should I use with a Flex-Hone?
Use 10–30 weight cutting oil or dedicated Flex-Hone Oil for most applications. For hydraulic brake cylinders only, use hydraulic brake fluid. Never use kerosene, WD-40, or run the tool dry. Using grease instead of oil produces a finer surface finish.
What RPM should I use for Flex-Hone tools?
RPM depends on diameter. Small tools (under 25mm) can run to 1200 RPM. A 1" tool runs around 800 RPM. A 3" tool around 700 RPM. A 6" tool around 450 RPM. Larger tools run slower. Use 60–120 strokes per minute for 20–45 seconds per bore.
Can I use a Flex-Hone with a drill or CNC machine?
Yes — portable hand drills, drill presses, lathes and CNC equipment all work. Do NOT use air tools or high-speed drill motors, as excessive speed damages the abrasive globules and produces a poor surface finish.
What abrasive type is right for my material?
Silicon carbide (SC) — cast iron, mild steel, general engine applications. Aluminium oxide (AO) — aluminium, brass, non-ferrous metals. Diamond — ceramic and carbide materials. Boron carbide — hardened steel and titanium.
How do I clean the bore after Flex-Honing?
Clean immediately with warm or hot water and detergent using a brush to remove all abrasive residue. Do not use solvents or kerosene. Dry thoroughly and oil immediately to prevent rust.
Need Help Selecting the Right Flex-Hone?
Contact our Australian technical team for expert advice on series selection, grit choice and availability.
Need Help Choosing the Right Flex-Hone?
Contact our technical team for expert advice on Flex-Hone sizing, grit selection and availability for your specific application.