The dimensions given for diameter at root of threads are also those for diameter of hole in nuts and diameter of lap drills. All bolts and studs 3/4 in. diameter and above, screwed into boilers, have 12 threads per inch, sharp thread, a taper of 1/16 in. per 1 inch; tap drill should be 9/64 in. less than normal diameter of bolts.
The table is based upon the following general formulae for certain dimensions:
Short diam. rough nut or head = 11/2 diam.
of bolt + 1/8.
" finished nut or head = 11/2 diam. of bolt + 1/16.
Thickness rough nut = diameter of bolt.
Thickness finished nut = diameter of bolt — 1/16.
Thickness rough head = 1/2 short diameter.
Thickness finished head = diameter of bolt — 1/16.
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[Illustration: AN ENGLISH RAILWAY FERRY BOAT.]
The illustrations above represent a double screw steam ferry boat for transporting railway carriages, vehicles, and passengers, etc., designed and constructed by Messrs. Edwards and Symes, of Cubitt Town, London. The hull is constructed of iron, and is of the following dimensions: Length 60 ft.; beam 16 ft.; over sponsons 25 ft. The vessel was fitted with a propeller, rudder, and steering gear at each end, to enable it to run in either direction without having to turn around. The boat was designed for the purpose of working the train service across the bay of San Juan, in the island of Puerto Rico, and for this purpose a single line of steel rails, of meter gauge, is laid along the center of the deck, and also along the hinged platforms at each end. In the engraving these platforms are shown, one hoisted up, and the other lowered to the level of the deck. When the boat