To meet the conditions of transmission work a change in both the shape and size of pins is necessary. In the first place, the shoulder on pins where the shank and stem meet, that relic of telegraph practice, should be entirely discarded. This change will save considerable lumber on pins of a given diameter at the shank, and will increase the strength of the pin by avoiding the sharp corner at the junction of the shank and stem.
Another change of design should leave an excess of strength in the stem of the pin, to provide for deterioration of the wood, and particularly for charring by current breakage. This increase of diameter and strength near the top of the pin will cost nothing in lumber, for the wood is necessarily there unless it is turned off. The shank of each pin should be proportionately shorter than in the older type, and the pin hole should be bored only part way through the cross-arm. A saving in lumber for pins and for cross-arms will thus be made, since the size of the cross-arm may be less for a given resistance to splitting.
With these changes in general design the pin is a simple cylinder in the shank, with a gentle taper from the shank to form the stem. An example of this design, which might well serve as a basis for a line of standard pins, would be a pin 2 inches in diameter and 3-1/2 inches long in the shank, and tapering for a length of 5 inches from the shank to form the stem, with a diameter of 1-1/2 inches at the top. The hole in a cross-arm for this pin should be 3-1/2 inches deep, and this, in an arm 4-3/4 inches deep, would leave 1-1/4 inches of wood below the pin. From the lower end of the pin hole, a hole 1/4-inch in diameter should run to the bottom of the cross-arm to drain off water. A line of longer pins designed to resist the same line pull as this short one would be strong enough for small conductors, say up to No. 1 B. & S. gauge wire.
For larger wires, long spans and sharp angles in a line, a pin 2-1/4 inches in diameter and 4-1/2 inches long in the shank, tapering for 5 inches to a diameter of 1-3/4 inches at the top, or longer pins of equal strength, should be used.
Where the pin holes do not extend through the cross-arm there is no need of a shoulder on the pin to sustain the weight of the line wire. In the cross-arm on the new Niagara Falls line each pin hole is bored to a depth of 5 inches, leaving 1 inch of wood below the hole. On the line from Electra to San Francisco the depth of each pin hole is again 5 inches, and the depth of the cross-arm 6 inches.