Abstract: A percussion boring tool is disclosed for boring in the earth at an angle or in a generally horizontal direction. The tool has a steering mechanism substantially as shown in a copending patent application and a cylindrical body with overgage sleeves located over a portion of the outer body affixed so that they can rotate but cannot slide axially. The overgage areas at the front and back of the tool, or alternately, an undergage section in the center of the tool body permits a 2-point contact (front and rear) of the outer housing with the soil wall as opposed to the line contact which occurs without the undercut. The 2-point contact allows the tool to deviate in an arc without distorting the round cross-sectional profile of the pierced hole. Thus, for a given steering force at the front and/or back of the tool, a higher rate of turning is possible since a smaller volume of soil needs to be displaced.

Abstract: An insulated drill collar gap sub for a toroidal coupled telemetry system comprising a first annular sub member (100) operable to be connected at one end to a drill collar and a second annular sub member (104) operable to be connected at the other end to the drill collar. The first and second annular sub members have longitudinally extending interconnecting structural members (106, 118) operable to structurally interfere. The interconnecting structural members are dimensioned to form a continuous gap (116) between mutually opposing surfaces and a dielectric material (118) fills the gap to electrically isolate the first annular sub member (100) from the second annular sub member (108). A bearing member (124) is positioned between the first annular member and the second annular member but is insulated from at least one of said annular members to facilitate the formation of a drill collar of structural and electrical integrity.