Flex-Hone GB31224 3-1/2ft 240 Grit Silicon Carbide - Precision Finish

In this review of the Flex-Hone GB31224, the bottom line is straightforward: this 3-1/2' 240 grit silicon carbide hone is for mechanics and machinists who need a reliable, oil-retaining crosshatch finish on mild steel, stainless, cast iron and other softer ferrous materials. The reviewer found it especially useful for rebuilding hydraulic and engine cylinders where a true plateau finish and consistent grit size matter. It is a quality, USA-made option that simplifies deburring and surface prep while producing repeatable results when used with the correct bore size.

Key Features

• Made in the USA: Built by the original inventor, the tool offers consistent manufacturing quality and durability you can rely on in a professional shop.
• Engineered oversize design: The intentionally oversized construction makes the tool self-centering and self-aligning for easier use and more uniform contact across the bore.
• 240 grit silicon carbide abrasive: Delivers a fine plateau finish typically in the 24-32 microinch range, suitable for oil retention and smooth sliding surfaces.
• Crosshole deburring capability: Finishing and deburring are accomplished in a single setup, saving time on valves, pumps and cylinder work.
• Versatile mounting: Works in a hand drill, drill press or CNC spindle so it integrates into common shop workflows with minimal fuss.
• Specified fit: Supplied for 3.251'-3.500' bores with a 0.310' shank and 13.5' overall length for predictable compatibility.

Who It's For

The Flex-Hone GB31224 is aimed at engine rebuilders, hydraulic technicians and home machinists who need a fast way to restore cylinder walls and create an oil-holding crosshatch. It performs best when used for mid-size bores in the specified diameter range and where a plateau finish is preferred over aggressive material removal.

Those who should look elsewhere include users needing heavy stock removal or abrasive action on very hard alloys beyond the intended softer ferrous materials. Also, if you do not have access to a stable rotating spindle or proper speed control, results may be inconsistent.

Pros & Cons

Pros

• Produces a uniform plateau crosshatch that improves lubrication retention and sliding action.
• Easy to use and self-centering, which reduces fixturing time and alignment fuss.
• Durable construction with consistent grit for repeatable finishes across multiple uses.
• Combines deburring and finishing in one pass, saving operational time.

Cons

• Not intended for heavy stock removal; it is a finishing tool rather than a cutter.
• Requires correct bore sizing and a suitable spindle speed for best results.

Specifications

Product	GB31224 FLEX-HONE
Diameter	3.500' (89mm)
Abrasive	240 grit silicon carbide
Intended materials	Mild steel, stainless steel, cast iron and softer ferrous materials
Fit bore range	3.251' - 3.500'
Shank and length	0.310' shank, 13.5' overall length
Typical finish	24 - 32 Microinch (0.6 - 0.8 Micrometer)

Our Verdict

The Flex-Hone GB31224 is a dependable finishing tool for anyone rebuilding cylinders or prepping bores for seals and rings. It offers clear value for its intended use thanks to a proven design, consistent 240 grit abrasive and easy operation. Buy it if you need a repeatable plateau finish and oil-retaining crosshatch in the specified bore range; skip it if you need aggressive material removal or work outside the supported materials.

Frequently Asked Questions

What bore sizes does this hone fit?
It is designed for bores between 3.251' and 3.500'.

Can it be used in a hand drill?
Yes, it can be run in a hand drill, drill press or compatible CNC spindle with appropriate speed control.

What finish will it produce?
The 240 grit silicon carbide typically yields a plateau finish of about 24-32 microinch, ideal for oil retention.