Types and Uses

TM 9-243 TYPES AND USES PLUMB BOBS A plumb bob is a precision instrument used to establish a true vertical transfer and line-up reference point, and to take readings or soundings in tanks and voids. Plumb bobs are used by carpenters, surveyors and mainte- nance technicians. SURVEYOR'S POLISHED BRASS The surveyor’s brass plumb bob may be either a spool type (A) or an adjustable cap type (B). Both types have replaceable steel points for increased accuracy. The adjustable cap allows the operator to make minor cor- rections to height and rotation to make sure the bob hangs straight. The surveyor’s brass plumb bob comes with a minimum of 7 feet of nylon, silk or linen cord. It comes in 6, 8, 10, and 16 ounce sizes. The heavier plumb bobs are better for use in windy areas. SOLID STEEL The solid steel plumb bob (A) may have a machined integral head, body, and point. It may have just a remov- able head (B), or a removable head and a replaceable point (C). It may be round or hexagonal in shape and it comes in 3, 8, and 12 ounce sizes. Cord for the solid steel bobs must be obtained from a separate source. This type plumb bob is used when extreme accuracy is not required. 11-2