Rivet spacing, also referred as rivet pitch, is the distance between the rivets in the same row, and is measured from the rivet center to the rivet center. Transverse pitch is the distance between the rows of rivets, and is measured from the rivet center to rivet center. Edge distance is the distance from the center of the rivet to the edge of the material being riveted.

Figure 13-43.-Rivet length.

There are no specific rules that apply to every case or type of riveting. There are, however, certain general rules that should be followed.

RIVET SPACING. Rivet spacing (pitch) depends upon several factors, principally the thickness of the sheet, the diameter of the rivets, and the manner in which the sheet will be stressed. Rivet spacing should never be less than three times the rivet diameter. Spacing is seldom less than four times the diameter nor more than eight times the diameter.

TRANSVERSE PITCH. When two or more rows of rivets are used in a repair job, the rivets should be staggered to obtain maximum strength. The distance between the rows of rivets is called "transverse pitch." Transverse pitch is normally 75 percent of existing rivet pitch, but should never be less than 2 1/2 times the diameter.

EDGE DISTANCE. The edge distance for all rivets, except those with a flush head, should not be less than twice the diameter of the rivet shank nor more than four times the diameter of the rivet shank. Flush-head rivets require an edge distance of at least 2 1/2 times the diameter. If rivets are placed to close to the edge of the sheet, the sheet is apt to crack or pull away from the rivets. If they are placed too far away from the edge, the sheet is apt to turn up at the edge.

NOTE: On most repairs, the general practice is to use the same rivet spacing and edge distance that the manufacturer used in the surrounding area, or the structural repair manual for the particular aircraft may be consulted, Figure 13-44 shows rivet spacing and edge distance.

Figure 13-44.-Rivet spacing and edge distance.