The endurance of the gear teeth is also a question to be decided by use. It has been said that “the teeth are so designed as to be relatively stronger than the cranks and under excessive strain the cranks will break first;” also that “the individual parts are stronger than the elementary parts of the chain.” We have seen cranks tested, in regular shop routine, by samples taken out of each small lot, under a measured load of 1,000 pounds, and have seen them show their quality by returning to the straight line when the load was removed. The cross-section of an average crank is three to five times that of a bevel or radial tooth. In practice, cranks do not break; some other part, less strong, breaks when something must, and so the statement that the 안전놀이터 bevel tooth is stronger than the crank which is to be measured against it under load seems rather too forcible. The comparatively slight tooth must bear the same strain which comes on other parts and the very small though real bit of elasticity or “give” which the chain possesses, by virtue of being made up of many parts joined together, is lacking in gears of any kind; the strain on those is “solid” and unrelieved. The fact that breakage of a sprocket (unless by some collision or extraordinary fall) is a mishap almost unheard of does not insure the gear tooth in the least—the two are not the same case. The sprocket tooth is very thick in the direction of the strain, and the pull of the chain comes on not less than five teeth at once on the rear sprocket and twice as many on the front, thus dividing the load; the gear teeth, on the contrary, are thin, and the strain is concentrated on not more than two at a time, practically upon one. Yet we must distinguish here the bevel and the spur-gear tooth from the peculiar teeth on the pin-roller gear; the latter are so thick that no doubt of their strength need be raised.