Bronze or iron butts, especially if "they have a loose joint, should have the bearing surfaces fitted with some form of steel washer, to reduce the wearing of the bearings. In loose-joint butts the washers are exposed as in Fig. 343 ; in loose-pin butts the more general custom is to countersink the washers in the hubs of the butt, so as not to show externally. With wrought steel butts washers are unnecessary except for very heavy doors. The Stanley Works have recently patented a ball-bearing washer for their butts, to be used for very heavy doors, which greatly reduces the friction and increases the wearing quality. Two of these washers are used on loose-pin butts (see Fig. 345) and one on the loose-joint butts. The balls are made of the hardest steel and there is no danger of their crushing. An enlarged view of the washer is shown in Fig. 344.
The Yale bronze butts are fitted with self-lubricating steel washers, which are perforated and filled with a non-fluid lubricant, which prevents wear and creaking.
Sizes. - Butts are made in sizes varying by half inches from 3x3 to 5½ x 5½, and above that by inches to 8x10 inches. Larger than 6x6 inches are seldom used, as it is much better to increase the number of butts rather than the size.
In specifying the sizes, 3 ½ x 3½-inch butts may be used for 1 3/8-inch pine doors not over 2 feet 8 inches wide; 4x4 butts for doors 1 ¾ inches thick and 7 feet high, and 4½ or 5-inch butts for heavier doors. Doors over 7 feet 6 inches high should be hung with three butts, and it would be better to hang a 7-foot door with three 4x4 butts than with two 5x5, as the three butts will not permit the door to spring in the middle.
It sometimes happens that a 4x4 butt will not allow the door to swing back parallel with the wall without striking the trim of the door. For such cases butts wider than they are high are made, as 4½x4 and 5x4. The butts should always project beyond the face of the door sufficient to throw the door out beyond the trim, as shown in Fig. 346.
The outside doors of public buildings should always open outward, and should be hung so as to swing back out of the way, and provided with a hook or other means of keeping them open when desired.