N.Y. Comp. Codes R. & Regs. tit. 12, § 23-5.12 – Horse scaffolds.

(1) The minimum sizes of members for horse scaffolds used for light duty shall be two inches by four inches for the backs or bearers and one inch by four inches for the legs and horizontal braces. The span of such backs or bearers shall not exceed four feet.
(2) The minimum sizes of members of horse scaffolds used for medium duty shall be one and one-quarter inches by nine inches for the backs or bearers and one and one-quarter inches by four and one-quarter inches for the legs and horizontal braces. The span of such backs or bearers shall not exceed six feet.
(3) The minimum sizes of members of horse scaffolds used for heavy duty shall be three inches by four inches for the backs or bearers and one and one-quarter inches by four and one-quarter inches for the legs and horizontal braces. The span of such backs or bearers shall not exceed six feet.
(4) The backs or bearers of horse scaffolds shall in every case rest on gusset braces which are at least one inch thick.
(5) Every horse scaffold shall be provided with sufficient diagonal and horizontal bracing to assure rigidity.
(6) In lieu of wood, the legs of such horses may be constructed of metal which is in every case equivalent in strength to the wood herein required.
(7) Horse scaffold legs may be lengthened by means of splicing on extension pieces having the same cross-sectional areas as the scaffold legs, provided such extension pieces lap the full lenghts of the scaffold legs and are securely attached to the legs by through bolts.
(d) Horse spacing.
The backs or bearers or horses used in the construction of scaffolds designed for loads up to 25 pounds per square foot shall be spaced not to exceed 10 feet, center to center. When used in scaffolds designed for loads up to 50 pounds per square foot such spacing shall not exceed eight feet, center to center. When used in scaffolds designed for loads up to 75 pounds per square foot such spacing shall not exceed six feet, center to center.

(a) Limitation of height.

Horse scaffolds shall not be constructed with more than two tiers of horses and the height of the working platforms of such scaffolds shall not exceed 10 feet.

(b) Installation of horse scaffolds.

The footings for horses shall be level and secure against accidental movement in any direction. Where horse scaffolds are superimposed upon other types of scaffolds, the horses shall be placed directly over supporting beams. All horse scaffolds shall be secured against sliding or tipping.