General Application and Selection of the Flex-Hone® Tool

General info | size selection | abrasive types | finishes and grit selections | rpm and stoke | lubricant | tool life

This is only a general guide. For specific applications and recommendations
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The Flex-Hone Tool is a resilient, flexible honing tool used to improve the internal surface finish of a bore or cylinder. It is comprised of abrasive globules laminated onto the ends of flexible nylon filaments. It's unique construction allows the tool to be self-aligning, self-centering and self-compensating for wear. The tool provides the benefit of removing loose, torn and folded metal and creating a substantially flat or plateau surface. An additional important application for the Flex-Hone Tool is burr removal from cross-drilled holes.

The Flex-Hone Tool is manufactured in 8 different abrasive types and 11 different grit selections in a wide selection of sizes to work on a broad variety of base materials and surface finish requirements. The tool is produced in diameters from 4mm to 36".




Tool diameter is determined by the nominal bore size in which the tool is to operate. The Flex-Hone tool is always produced and used in an oversize condition. The degree of oversize creates a soft cutting action. For example, a 1" Flex-Hone size is ordered if a 1" bore is to be finished and the tool is provided oversized. If the bore size is between standard Flex-Hone sizes, the next larger standard Flex-Hone should be selected. For instance, if the nominal bore is 1.093", then the 1-1/8" Flex-Hone is ordered.



Abrasives Types

Abrasive selection is largely dependent on the base material being finished and whether the application is for surface finishing or deburring.

Silicon carbide is by far the most popular abrasive type. It is used to finish mild steel, stainless steel and cast iron.

Aluminum Oxide is the next most popular abrasive and it is used to finish non ferrous materials like aluminum, brass, bronze, softer metals and plated cylinders.

Zirconia Alumina (Z-Grain) has very similar cutting properties to silicon carbide and can generally offer longer tool life. It is available in two grades: #1525 (25% Zirconia, 75% Alumina) and #1549 (40% Zirconia and 60% alumina). It is used to finish low carbon to medium carbon steels, stainless steel and cast iron.

Boron Carbide is used to finish medium to high carbon steels and heat-treated steels to 50 Rc. It is also useful in titanium, Inconel and Monel. Tungsten Carbide is used for the high carbon steel alloys and more exotic space age alloys.

Levigated Alumina is a super fine abrasive used for a final polish on many materials. This abrasive should be used where Ra requirements are very low.

Diamond is used  for carbide, ceramic, hardened tool steel and heat treated steels above 51 Rc

Available grits and abrasives marking


ABRASIVE TYPES  20 40 60 80 120 180 240 320 400 600 800
SC=Silicon Carbide   x x x x S S S S x x x
AO=Aluminum Oxide  x x x x x x x x x x x
BC=Boron Carbide  x x x x x x x x x x x
WC=Tungsten Carbide
(either 100% or 50/50)
  x x x x x x x x + + +
Z Grain=Alumina Zirconia
No. 1525 (25% Zirconia/75% Alumina)
  + + x x x x x x + + +
Z Grain=Alumina Zirconia
No. 1549 (40% Zirconia/60% Alumina)
  + + + + x x x x + + +
LA=Levigated Alumina   Available in extra fine grit only

"S" denotes grit is standard
"x" denotes grit is available
"+" denotes grit in unavailable

The Flex-Hone®Tool is manufactured in an extensive range of abrasive types and grit sizes. The Flex-Hone®Tool is color coded for convenient identification. The color code consists of a colored end marking and a band of color around the stem, just under the head of the hone.

Flex-Hone® Color Code

Stem Marking Type of Abrasive Symbol    End Marking Grit Size  End Marking Grit Size
No Color Silicon Carbide SC    Brown 20  Navy Blue 240
Black Aluminum Oxide AO    Purple 40  White 320
Gold Boron Carbide BC    Gray 60  Yellow 400
Tan Tungsten Carbide WC    Orange 80  Pink 600
Green Levigated Alumina LA    Silver (no color) 120  Light Blue 800
Red Zirconia Alumina Z-Grain #1525    Cardinal Red 180       
White Zirconia Alumina Z-Grain #1549             




The amount of work to be performed and the degree of surface finish improvement required govern grit selection. Coarse finishes may require progressively finer Flex-Hones to meet final surface finish requirements. In very general terms, final finish will be in the following ranges. This chart is intended to offer a starting point in selecting a grit but the final selection must be verified by actual trial.


Grit Finish Range
800-LA Ra 3-10 (0.05 - 0.2 Micrometer)
600 Ra 8-12 (0.2 - 0.3 Micrometer)
400 Ra 10-20 (0.3 - 0.6 Micrometer)
320 Ra 18-30 (0.5 - 0.7 Micrometer)
240 Ra 24-32 (0.6 - 0.8 Micrometer)
180 Ra 30-40 (0.7 - 1.0 Micrometer)
120 Ra 35-50 (0.9 -1.4 Micrometer)
80 Ra 45-64 (1.2 - 1.6 Micrometer)
60 Ra 60-80 (1.5 - 2 Micrometer)
40 Ra 70-125 (1.7 to 3.2 Micrometers)
20 Ra 125-250 (3.2 to 6.3 Micrometers)




RPM and Stroke rate

The Flex-Hone tool is a low RPM tool. Specific RPM is dependent on the diameter of the tool and the application. General speed ranges are given but, again, machine trials are required to verify the parameters.

Hone Dia. RPM
19" to 36" 60-120 RPM
12" to 18" 80 to 350 RPM
8" to 12" 300 to 500 RPM
4" to 8" 400 to 600 RPM
2" to 4" 600 to 800 RPM
½" to 2" 700 to 900 RPM
4mm to ½" 800-1200 RPM

Stroke rate is a function of Flex-Hone diameter, stroke length and cross hatch angle specification, if any. High crosshatch angles require faster stroke rates. The larger diameter tools might feed as slow as10-12 IPM while the smaller diameter tools with high cross hatch angles might require feed as high as 250 IPM.

The hone can be made to rotate in both directions. Often this is preferable to do on each work piece (i.e. 5 strokes clockwise, 5 strokes counterclockwise)




The Flex-Hone tool always requires the use of a lubricant or honing oil. Finer surface requirements dictate better quality honing fluids be used. Many fluids may be used general applications: water soluble oils, mineral oils, motor oils and cutting and tapping fluids are adequate to keep the tool from loading and to insure exposure of fresh cutting particles. Solvents should be avoided, as they tend to degrade the adhesive bond in the tool.



Tool Life

The Flex-Hone can be used until there is virtually no abrasive left on the filaments. Cutting curves can be plotted to show when to replace the tool. Many users will increase the number of strokes used at a point in the tool wear to compensate. Tool life can be increased if the tool is reversed every 4th or 5th part. It is also effective to reverse the tool a portion
of the cycle if cross drilled holes are present.


link to Flex-Hone® index page


How To Use a Flex-Hone Tool

March 2022, October 2020, Feb 2020, updated December 2019, May 2012 CSS, April 2009, March 2006

The descriptions, illustrations, specifications, dimensions, and part numbers are subject to change without notice.

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