Assembly comprising, on a turbomachine:—a combustion chamber (30) having a longitudinal axis (30a) and comprising: internal and external longitudinal walls (90) having a first opening (90a) substantially transverse to said axis (30a), an outer casing (110) having a second opening (110a) likewise substantially transverse to said axis (30a),—a turbomachine sparkplug (150),—a device (130) for radially securing the sparkplug (150), which device (130) comprises a sparkplug adapter (160) fixed toward a first end to the outer casing (110), facing the second opening (110a) and through which adapter and casing the sparkplug (150) in question passes, and a sparkplug guide (190) kept in contact with the external longitudinal wall (90), facing the first opening (90a) and through which the sparkplug (150) passes to emerge in the combustion chamber (30), the sparkplug (150) and the sparkplug guide (190) each having a screw thread (103, 105), the screw threads (103, 105) being screwed together so as to stabilize the sparkplug (150) radially to the axis (30a) of the combustion chamber (30) with respect to said external longitudinal wall (90), and—in this condition, the sparkplug (150) and the sparkplug guide (190) are mounted freely with respect to the outer casing (110) in a direction substantially radial to the axis of the second opening (110a).