OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

March 1, 1992

Mr. Stan Rodrigues Makita
U.S.A., Inc.
44388 Old Warm Springs Blvd.
Fremont, California 94538-6148

Dear Mr. Rodrigues:

Thank you for your letter of October 4, 1991 and your follow-up letter of October 9, 1991 requesting an interpretation of the general flange requirements applicable to 4 inch (10.16 cm), type 27 abrasive wheels which are subject to 29 CFR 1910.215(c) standards. Please accept our apologies for the delay in response.

The general requirement at 29 CFR 1910.215(c)(1) requires that all abrasive wheels be mounted between flanges which "shall not be less than one-third the diameter of the wheel." At 29 CFR 1910.215(c)(4)(i) the standard requires that "both flanges, of any type, between which a wheel is mounted, shall be the same diameter and have equal bearing surface." For an abrasive wheel 4 inches (10.16 cm) in diameter, at least 1.33 inch (3.38 cm) flanges are required.

The standard provides an exception to 29 CFR 1910.215(c)(1) and .215(c)(4)(i); it requires type 27 reinforced organic bonded abrasive wheels to be mounted in accordance with 29 CFR 1910.215(c)(4)(ii). This latter application permits an adaptor nut (in place of the outer or front flange) to be less than the minimum one-third diameter of the wheel when the inner or back flange extends beyond the central hub or raised portion and contacts the wheel to counteract the side pressure, that is, the applied force distributed over the contact area at the periphery of the wheel. Extension of the back flange beyond the central hub raised portion and through the curved area stiffens the abrasive wheel to prevent bending and provides a reactive pressure to the applied pressure which is transmitted to the grinder.

The Underwriters Laboratories (UL) Standard 45-Portable Electrical Tools, dated January 10, 1985 includes flange standards for grinder wheels. Copies of pages from the UL Standard 45 enclosed in your letter appear to be compatible with the Occupational Safety and Health Administration (OSHA) standards at 29 CFR 1910.215(c). Originally, 29 CFR 1910.215(c) was adopted from the American National Standards Institute (ANSI) standards, that is, ANSI B-7.1-1970, "Safety Code for the Use, Care and Protection of Abrasive Wheels". Although ANSI has updated its standard since the 1970 edition, OSHA has not.

Under an OSHA policy for "de minimis" violations, employers are allowed to abide by the most current consensus standard applicable to their operations, rather than with the OSHA standard in effect at the time of the inspection, when the employer's action provides equal or greater employee protection. "De minimis" violations are violations of existing OSHA standards which have no direct or immediate relationship to safety or health. Such violations of the OSHA standards result in no citation, no penalty and no required abatement.

Under the policy of "de minimis" violations employers who fully comply with the grinder wheel configuration requirements of American National Standards Institute (ANSI) standards, that is, ANSI B-7.1-1988, "Safety Code for the Use, Care and Protection of Abrasive Wheels" would not be cited under 29 CFR 1910.215(c) standards. Relating to these ANSI configuration requirements, the following comments are applicable to the grinder wheels depicted in the brochures enclosed in your October 4, 1991 letter.

The type 27 grinding wheel requires a specially designed adaptor except when the wheel is 5 inches (12.70 cm) or less in diameter and has a 7/8 inch (2.22 cm) diameter arbor hole. In all other cases, the adaptor (back flange) must extend beyond the central hub or raised portion and contact the wheel to counteract the side pressure on the wheel in use. The OSHA standard at paragraph (c)(4)(ii) describes the shape and size of the adaptor and contains other pertinent information. The diameter of this adaptor must be a minimum of one-third (1/3) the diameter of the wheel. The flange described in paragraph (c)(1) is an exception because the front flange (actually the adaptor nut) must be less than 1/3 the diameter of the wheel so that it can fit within the central cavity of the wheel and not extend above the face of the wheel. This recessed fit is necessary to provide peripheral grinding, free from surface protrusions.

The 1988 revision of the ANSI standard for abrasive wheels (ANSI B7.1) has more detail than the 1970 edition from which OSHA developed its standard. The 1988 ANSI standard discusses the requirements for flanges for No. 27 grinding wheels in paragraph 5.1.2. In subparagraph, the standard contains a discussion of flanges for No. 27 wheels larger than 5 inches (12.70 cm) in diameter. In subparagraph, the standard discusses flanges for wheels 5 inches (12.70 cm) or less in diameter having arbor holes of 3/8 inch (0.95 cm) or 5/8 inch (1.59 cm) in diameter, and separately, those having arbor holes of 7/8 inch (2.22 cm) in diameter. For abrasive wheels, 5 inches (12.70 cm) or less in diameter, with 3/8 inch (0.95 cm) or 5/8 inch (1.59 cm) diameter arbor holes, the adaptor must meet the requirements of paragraph referenced previously. For abrasive wheels, 5 inches (12.70 cm) or less in diameter, with 7/8 inch (2.22 cm) diameter arbor holes, the wheel may be mounted between matched flanges (those of equal diameter) provided the diameter of the flanges are at least 1.62 inches (4.12 cm) in diameter, that is, at least one-third (1/3) the diameter of the wheel.

Thank you for pointing out to us differences in interpreting these standards. We will provide copies of your letter and this response to all our Regional technical support staffs. Also, we will add this correspondence to our interpretation data base for future access.

We appreciate your interest in employee safety and health. If we can be of further assistance, please do not hesitate to contact us.


Patricia K. Clark, Director
Directorate of Compliance Programs