A downhole assembly (25, 125), comprising: 1.1 a centralizer (28, 128), comprising 1.2 an elongated tubular member having a wall formed to provide a cross-section that provides first outwardly-convex and inwardly-concave lobes (38, 128B), the first lobes (38, 128B) arranged to contact a bore wall of a bore (27, 127) in a section (26, 126) of drill string at a plurality of spots spaced apart around a circumference of the bore wall; and 1.3 a plurality of inwardly-projecting portions, each of the plurality of inwardly-projecting portions arranged between two adjacent ones of the plurality of first lobes (38, 128B); and further comprising: 1.4 a drill string section (26, 126) having a bore (27, 127) extending longitudinally through the drill string section (26, 126), wherein the drill string section (26, 126) comprises a drill collar; 1.5 a downhole probe located in the bore (27, 127) of the section (26, 126), wherein the probe is slidable longitudinally into the centralizer and is locked against rotational movement relative to the centralizer (28, 128); and 1.6 wherein the centralizer (28, 128) is in the bore (27, 127), the wall of the centralizer (28, 128) extending around the downhole probe, the wall formed to contact an inside surface of the bore (27, 127) and an outside surface of the downhole probe, a cross-section of the wall following a path around the downhole probe that zig zags back and forth between the outside surface of the downhole probe and the inside surface of the bore wall. 1.1 a centralizer (28, 128), comprising 1.2 an elongated tubular member having a wall formed to provide a cross-section that provides first outwardly-convex and inwardly-concave lobes (38, 128B), the first lobes (38, 128B) arranged to contact a bore wall of a bore (27, 127) in a section (26, 126) of drill string at a plurality of spots spaced apart around a circumference of the bore wall; and 1.3 a plurality of inwardly-projecting portions, each of the plurality of inwardly-projecting portions arranged between two adjacent ones of the plurality of first lobes (38, 128B); and further comprising: 1.4 a drill string section (26, 126) having a bore (27, 127) extending longitudinally through the drill string section (26, 126), wherein the drill string section (26, 126) comprises a drill collar; 1.5 a downhole probe located in the bore (27, 127) of the section (26, 126), wherein the probe is slidable longitudinally into the centralizer and is locked against rotational movement relative to the centralizer (28, 128); and 1.6 wherein the centralizer (28, 128) is in the bore (27, 127), the wall of the centralizer (28, 128) extending around the downhole probe, the wall formed to contact an inside surface of the bore (27, 127) and an outside surface of the downhole probe, a cross-section of the wall following a path around the downhole probe that zig zags back and forth between the outside surface of the downhole probe and the inside surface of the bore wall. 1.4 a drill string section (26, 126) having a bore (27, 127) extending longitudinally through the drill string section (26, 126), wherein the drill string section (26, 126) comprises a drill collar; 1.5 a downhole probe located in the bore (27, 127) of the section (26, 126), wherein the probe is slidable longitudinally into the centralizer and is locked against rotational movement relative to the centralizer (28, 128); and 1.6 wherein the centralizer (28, 128) is in the bore (27, 127), the wall of the centralizer (28, 128) extending around the downhole probe, the wall formed to contact an inside surface of the bore (27, 127) and an outside surface of the downhole probe, a cross-section of the wall following a path around the downhole probe that zig zags back and forth between the outside surface of the downhole probe and the inside surface of the bore wall.