• The system shall be integrated into a single unit of rigid aluminum. • The base may be cast or machined and shall have been stress relieved prior to machining to maintain a bottom surface which is flat within 0.005 inches over the entire surface of the instrument. Torquing of the top shell or any other part of the system to maintain flatness in the base will not be allowed. Attachment of the top shell must not cause any deformation to the base or bottom surface of the instrument. • The upper shell or housing shall be constructed of a material durable enough to protect the internal electronic components and shall be water and dust resistant. If the shell or housing is painted, it must be painted with an epoxy paint, which will not chip or peel under normal field conditions. Powder coated finishes are acceptable. • Positioning of the source rod, for backscatter and direct transmission density testing, shall be accomplished using an index rod. The index rod shall be mounted securely to the base of the instrument without any staking, shimming or epoxy. The index rod shall be placed in the base of the instrument such, that the height of the source rod tip, capsule end, is 0.010 inches +/- 0.005 inches above the test area when the source rod is in the backscatter testing position. The source rod handle shall be centered over the index rod so there is no contact between the source rod handle and the index rod other than the trigger mechanism. In the standard count position, the free end of the source rod handle shall have a maximum side play in either direction of 0.500 inches. There shall be no alternative mechanism used in place of the index rod that completely or partially encloses the source rod. • The source rod must be removable with hand tools so all bearings, seals and wipers may be cleaned and lubricated and, if necessary, said bearings, seals and wipers shall be replaceable with hand tool without index rod removal. No adhesives may be used which would prevent replacement of the above without damage to other metal parts.
