---
product_id: 149138050
title: "Brush Research GB31212 FLEX-HONE®, 3-1/2\" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials"
brand: "flex-hone"
price: "$141.33"
currency: USD
in_stock: true
url: https://www.desertcart.ec/products/149138050-brush-research-gb31212-flex-hone-3-1-2-89mm-diameter
store_origin: EC
region: Ecuador
---

# Self-centering & self-aligning design 3.5" diameter precision fit 120 grit silicon carbide abrasive Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials

**Brand:** flex-hone
**Price:** $141.33
**Availability:** ✅ In Stock

## Summary

> 🔧 Elevate your cylinder finish game—because flawless is the new standard.

## Quick Answers

- **What is this?** Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials by flex-hone
- **How much does it cost?** $141.33 with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.ec](https://www.desertcart.ec/products/149138050-brush-research-gb31212-flex-hone-3-1-2-89mm-diameter)

## Best For

- flex-hone enthusiasts

## Why This Product

- Trusted flex-hone brand quality
- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Plug & Play Setup:** Fits standard 3.25"-3.5" bores and works seamlessly with hand drills, CNC, or drill presses—no special training needed.
- • **Consistent Plateau Finish:** Delivers an oil-retentive crosshatch pattern that boosts seal life and reduces wear.
- • **Precision Engineered Oversize:** Ensures optimal pressure and perfect self-centering for flawless finishes every time.
- • **Versatile Material Compatibility:** Expertly hones mild steel, stainless steel, cast iron, and softer ferrous metals with ease.
- • **Dual-Action Finishing & Deburring:** Simultaneously smooths and deburrs crossholes, streamlining your workflow.

## Overview

The Brush Research GB31212 FLEX-HONE® is a 3.5" diameter, 120 grit silicon carbide honing tool designed for mild steel, stainless steel, cast iron, and softer ferrous materials. Its oversized, self-centering design ensures consistent pressure and a superior plateau finish with an oil-retentive crosshatch pattern. Ideal for rebuilding hydraulic, pneumatic, engine, and brake cylinders, it also deburrs crossholes in a single operation. Compatible with hand drills, drill presses, and CNC equipment, this USA-made tool streamlines finishing processes while extending seal life and improving performance.

## Description

The FLEX-HONE® tool was originally created by Brush Research Manufacturing to deglaze cylinder walls in automotive applications. Brush Research embraced the benefits of a plateau finish and pioneered the concept of plateau honing culminating in the introduction of the FLEX-HONE® tool in 1972. The FLEX-HONE® has gained many nicknames over the years and including ball hone, ball style hone, flexihone, dingleberry hone, bead brush, glaze breaker and glaze buster. Flexible honing with the FLEX-HONE® tool produces an oil holding cross hatch pattern and a true plateau finish free of cut, torn and folded metal. Any type or size of cylinder can benefit from the FLEX-HONE®. These abrasive bead style brushes are produced in standard diameters from 4mm to 36 inches. Nine abrasive types are offered including Silicon Carbide, Aluminum Oxide, Boron Carbide and Diamond allowing the tool to be tailored to finish any base material. A choice of 11 different grit selections are available for precise control of finish parameters. The elimination of peaks results in rapid ring seating, better oil control, reduced seepage in hydraulic and pneumatic applications and provides better seal performance and longer seal life. Successful applications include firearm chambers, shotgun barrels, musical instruments, combustion chambers, air compressors, pumps, valve bodies, valve guides, brake cylinders, wheel cylinders and the list goes on and on. FLEX-HONE® tools are also very effective for deburring cross drilled holes, port radiusing and edge blending. Because of its unique construction, the FLEX-HONE® is self-centering, self-aligning, and self-compensating for wear so it does not require an elaborate set-up or special training. Deburring can be effectively automated and combined in the machining process to allow a complete cylinder finish in one operation or it can be employed as a secondary operation with equal results.

## Features

- [QUALITY]-Proudly Made in the USA. Quality and consistency you can count on made from the inventors and makers of the tool.
- [DESIGN]-The FLEX-HONE is intentionally manufactured oversized. This engineered oversize creates the optimal amount of pressure inside the cylinder wall allowing the tool to be self-centering, self-aligning and self-compensating for wear and easy use.
- [FINISHING BENEFITS]-Offered in a wide variety of grits to achieve specific finishing tolerances as well as a beautiful crosshatch finish. Ideal for rebuilding hydraulic and pneumatic cylinders, engine and brake cylinders, valve guides, pumps, compressors and more.
- [CROSSHOLE DEBURRING]-Accomplish finishing and deburring simultaneously in a single setup. Can be used in virtually any rotating spindle from a hand drill, drill press or CNC equipment.
- [120 GRIT SILICON CARBIDE ABRASIVE]-Excellent on mild steel, stainless steel, cast iron and other softer ferrous materials. Typically achieves a finish of 35 - 50 Microinch (.9 - 1.4 Micrometer).
- [WHAT'S INCLUDED]-1 Each of a GB Standard Duty FLEX-HONE: 3.500" (89mm) Bore Diameter, 3.50" Abrasive Part Length, 0.310" Shank Diameter, 13.5" Overall Length. For Use on Bore Diameters Between 3.251"-3.500". PLEASE NOTE: ORDER BY BORE SIZE.

## Product Details

- **Material:** Silicon Carbide
- **Brand:** Flex-Hone
- **Grit Material:** Silicon Carbide
- **Bristle Type:** Abrasive Globule Bonded To Flexible Nylon Filament
- **Grit Type:** 120 Grit

## Images

![Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials - Image 1](https://m.media-amazon.com/images/I/61f9Ueb7-8L.jpg)
![Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials - Image 2](https://m.media-amazon.com/images/I/8156ob+ylqL.jpg)
![Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials - Image 3](https://m.media-amazon.com/images/I/71LI+vNqxIL.jpg)
![Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials - Image 4](https://m.media-amazon.com/images/I/81aPGQTXemL.jpg)
![Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials - Image 5](https://m.media-amazon.com/images/I/81X4pgWlJtL.jpg)

## Available Options

This product comes in different **Size, Style** options.

## Questions & Answers

**Q: Wish one is best for a cylinder wall that is 75mm (2.95 inch) ?**
A: For the cylinder wall bore size of 2.95", the 3" Flex-Hone is the correct choice., Enter this ASIN # B002N3AA2A  in the Amazon search bar for the correct hone.

**Q: Hello, my cylinder bore is 3 1/8" what size tool do i need to purchase thank you.**
A: For a 3.125" bore,  your application will require the 3-1/4" (3.250") diameter Flex-hone. The 3-1/4" will work perfectly in the 3-1/8" bore as the 3-1/4" Flex-hones working range is down to 3.000". Thank you for the inquiry.

**Q: Can i use this to hone out an old cast iron pipe?  it's about 3 3/4" now and i want it at 4" id. thanks**
A: This hone is not coarse enough to remove that much material. It would take forever and the hone would wear out first. You would need a lathe to remove that amount of thickness.

**Q: I see that it says tool is oversized. For a cylinder bore of 3.66, should I be getting the 3.75 or the 3.50 model?**
A: 1I bought a 4.50 and used it on a 3.55 bore with no problem I  didn't hone as much as instruction said for large bore, hatch marks were beautiful  so go bigger and you can use it over a broad area of bores.

## Frequently Bought Together

- Brush Research GB31212 FLEX-HONE®, 3-1/2" (89mm) Diameter, 120 Grit, Silicon Carbide, For Mild Steel, Stainless Steel, Cast Iron and Softer Ferrous Materials
- Brush Research FHQ FLEX-HONE® Oil, Specially Formulated Honing Oil, 1 Quart Bottle (32 fl oz)
- Permatex 81950 Ultra Slick Engine Assembly Lube, 4 oz. , Red

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*Product available on Desertcart Ecuador*
*Store origin: EC*
*Last updated: 2026-01-23*