A gas turbine engine installation comprising: a flexible printed circuit board harness arranged to transfer electrical signals around the engine installation; and at least one clip holding the printed circuit board harness, each clip comprising a generally U-shaped channel defined by a base with first and second sidewalls (220, 230) extending therefrom, wherein: the flexible printed circuit board harness is a thin, elongate member having upper and lower parallel major surfaces (24, 26) defined by a length (x) and a width (y), and a thickness (z) normal to the major surfaces; the first sidewall has a first side-tooth extending therefrom, and the second sidewall has a second side-tooth extending therefrom, the first and second side-teeth extending, from root to tip, in a direction that is substantially parallel to the plane of the base; and the base has a first set of base-teeth and a second set of base-teeth, with the first side-tooth and the second side-tooth extending in a direction that is generally perpendicular to the direction of the teeth of the first and second set of base-teeth such that a first portion of the flexible printed circuit board harness is gripped between tips of the first set of base-teeth and the first side-tooth, and a second portion of the flexible printed circuit board harness is gripped between tips of the second set of base-teeth and the second side-tooth. a flexible printed circuit board harness arranged to transfer electrical signals around the engine installation; and at least one clip holding the printed circuit board harness, each clip comprising a generally U-shaped channel defined by a base with first and second sidewalls (220, 230) extending therefrom, wherein: the flexible printed circuit board harness is a thin, elongate member having upper and lower parallel major surfaces (24, 26) defined by a length (x) and a width (y), and a thickness (z) normal to the major surfaces; the first sidewall has a first side-tooth extending therefrom, and the second sidewall has a second side-tooth extending therefrom, the first and second side-teeth extending, from root to tip, in a direction that is substantially parallel to the plane of the base; and the base has a first set of base-teeth and a second set of base-teeth, with the first side-tooth and the second side-tooth extending in a direction that is generally perpendicular to the direction of the teeth of the first and second set of base-teeth such that a first portion of the flexible printed circuit board harness is gripped between tips of the first set of base-teeth and the first side-tooth, and a second portion of the flexible printed circuit board harness is gripped between tips of the second set of base-teeth and the second side-tooth. the flexible printed circuit board harness is a thin, elongate member having upper and lower parallel major surfaces (24, 26) defined by a length (x) and a width (y), and a thickness (z) normal to the major surfaces; the first sidewall has a first side-tooth extending therefrom, and the second sidewall has a second side-tooth extending therefrom, the first and second side-teeth extending, from root to tip, in a direction that is substantially parallel to the plane of the base; and the base has a first set of base-teeth and a second set of base-teeth, with the first side-tooth and the second side-tooth extending in a direction that is generally perpendicular to the direction of the teeth of the first and second set of base-teeth such that a first portion of the flexible printed circuit board harness is gripped between tips of the first set of base-teeth and the first side-tooth, and a second portion of the flexible printed circuit board harness is gripped between tips of the second set of base-teeth and the second side-tooth.