without sharp teeth is shown pipe 250 is shown around centerline 252 slip insert 254 is touching the outside diameter 256 of pipe 250 and is contacting slip bowl 258 on the opposite side the contact surface 260 between slip insert 254 and slip bowl 258 is tapered at approximately eight degrees as is conventional in the art the coefficient of friction 262 at contact surface 260 and the coefficient of friction 264 at contact surface 266 between the slip insert 254 and the outer diameter 256 of pipe 250 are likely to be the same when pipe 250 is loaded downwardly by the force indicated as 268 slippage will occur at either at contact surface 260 or at contact surface 266 as the coefficient of friction is the same for both surfaces and the eight degree angle of surface 260 gives an additional resisting force the slippage will occur at surface 260 this is shown graphically with 270 being the normal perpendicular force to the surface 272 being the horizontal component of the force and 274 being the vertical component there is no comparable vertical component associated with the normal force to the contact surface 266 as the force is simply horizontal this means the pipe 250 will simply slip at contact surface 266 and fall rather than the slip insert 250 sliding down the taper and wedging more tightly to grip the pipe referring now to fig1 the same general geometry as was in fig1 is repeated however sharp teeth 280 are introduced at interface 282 it is a general industry practice to equate the effect of sharp teeth to be a coefficient of friction of 0 5 whereas the typical coefficient of friction at a surface like 284 to be 0 1 as the sliding friction force.