high  molecular  weight  hydrocarbons,  or  which asphalts, tars, pitches, and asphaltites are typical. BLASTING MAT– A heavy, flexible fabric of woven wire rope or chain, used to confine blasts. BLEEDING  OR  FLUSHING–   Is  the  upward movement  of  asphalt  in  an  asphalt  pavement, resulting in the formation of a film of asphalt on the surface.  The  most  common  cause  is  too  much asphalt in one or more of the pavement courses, resulting from too rich a plant mix, an improperly constructed seal coat, too heavy a prime or tack coat, or  solvent-carrying  asphalt  to  the  surface.  Bleeding or flushing usually occurs in hot weather. BLUE TOPS— Grade stakes with blue tops to indicate finish grade level, usually a 2-inch by 2-inch by 6-inch hub stake. BM— Bench mark. BODY— The load carrying part of a truck or scraper. BOGIE AXLE— Two or more axles, mounted to a frame so as to distribute the load between the axles and permit vertical oscillation of the axles. BOOM CHORD— A main corner member of a lattice type  of  boom. BOOM, CRANE— A long, light boom, usually of lattice construction. BOOM HOIST— Mechanism to control the elevation of the boom and to support it. BOOM LACING–  Structural truss members at angles to and supporting the boom chords of a lattice type of boom. BOOM, LATTICE—  A long, light boom fabricated of crisscrossed  steel  or  aluminum  angles  or  tubing. BOOM  LENGTH—  Boom length is a straight line through the center line of the boom pivot pinto the center line of the boom point load hoist sheave pin, measured  along  the  longitudinal  axis  of  the  boom. BOWL— (1) The bucket or body of a carrying scraper. (2) Sometimes the moldboard or blade of a dozer. BUCKET— A part of an excavator that digs, lifts, and carries dirt. BULLDOZER— (1) A tractor equipped with a front pusher blade. (2) In a machine shop, a horizontal press. CAPILLARY ATTRACTION—  The tendency of water to move into fine spaces, as between soil particles, regardless  of  gravity. CASING— A pipe lining for a drilled hole. CAT— (1)  A  trademark  designation  for  any  machine made  by  the  Caterpillar  Tractor  Company.  (2) Widely used to indicate a crawler tractor of any make. CAT HEAD—  A capstan winch. CATWALK— A pathway, usually of wood or metal, that gives access to parts of large machines. CENTRIFUGAL  FORCE—  Outward  force  exerted  by a body moving in a curved line. It is the force that tends to tip a car over in going around a curve. C-FRAME— An angling dozer lift and push frame. CHECK VALVE— Any device that will allow fluid or air to pass through it in only one direction. CHOKER— A chain or cable so fastened that it tightens on its load as it is pulled. CIRCLE REVERSE—  The  mechanism  that  changes  the angle of a grader blade. CLAM— A clamshell bucket. CLAMSHELL— (1) A shovel bucket with two jaws that clamp together by their own weight when it is lifted by the closing line. (2) A crane equipped with a clamshell  bucket. CLAMSHELL BUCKET— Usually consists of two or more similar scoops hinged together and a head assembly connected to the outer corners by struts. When the head and hinge are pulled toward each other, the scoops are forced together to dig and hold material. Control is by a holding line reeved over a boom  point  sheave  and  attached  to  the  head assembly to support the bucket in open position and usually  by  a  closing  line  also  reeved  over  a  boom point sheave, ending in a force amplifying tackle or other  means  between  the  head  assembly  and  scoop hinge to close the bucket. CLAMSHELL BUCKET, HYDRAULIC— Usually consists of two or more scoops hinged to a head assembly  housing  the  hydraulic  cylinder  or cylinders and the force amplifying linkage to open and close the scoops and to supply the digging force for the scoops. The bucket assembly is suspended from the boom by a rope. Because digging ability is largely  dependent  upon  bucket  weight,  buckets  are supplied in various weight classes which range from AI-2