A process for extracting a glow plug pencil or a broken pencil, the said pencil being stuck in the housing of the glow plug comprising a lower part and an upper part, the diameter of the upper part being greater than the diameter of the lower part, such that the housing has a shoulder, the pencil being stuck in the lower part of the plug housing, the process comprising the following steps: a) drilling a bore in the pencil in the longitudinal direction of the latter by means of a drill bit, the said drill bit comprising a drilling part having flutes and a rod, the diameter of the said drilling part being less than the diameter of the pencil; b) threading the bore drilled in step a) in the pencil by means of a tap, the said tap having a tapping part with at least one flute and at least one screwing tool and a rod, the diameter of the said tapping part being greater than the diameter of the bore and less than the diameter of the pencil; c) screwing an extractor into the said thread, the extractor comprising a threaded head by which it is screwed in the pencil and placed at one end of the rod; d) extracting the pencil by removing the extractor screwed into the pencil, and the drill bit is selected in such a manner that the diameter of its rod is greater than both, the diameter of its drilling part, such that the drill bit comprises a shoulder, as well as the diameter of the lower part of the plug housing, and in that step a) of drilling the bore comprises drilling the pencil until the said shoulder of the drill bit is positioned in abutment against the shoulder of the housing of the glow plug and the process being characterised in that step a) of drilling a bore is preceded by the installation of a centering pin at the orifice of the upper part of the plug housing for positioning one or more of the following elements: - a drill bit during the drilling operation of the pencil; - a tap during the threading of the bore; - an extractor while screwing it into the pencil thread. a) drilling a bore in the pencil in the longitudinal direction of the latter by means of a drill bit, the said drill bit comprising a drilling part having flutes and a rod, the diameter of the said drilling part being less than the diameter of the pencil; b) threading the bore drilled in step a) in the pencil by means of a tap, the said tap having a tapping part with at least one flute and at least one screwing tool and a rod, the diameter of the said tapping part being greater than the diameter of the bore and less than the diameter of the pencil; c) screwing an extractor into the said thread, the extractor comprising a threaded head by which it is screwed in the pencil and placed at one end of the rod; d) extracting the pencil by removing the extractor screwed into the pencil, and the drill bit is selected in such a manner that the diameter of its rod is greater than both, the diameter of its drilling part, such that the drill bit comprises a shoulder, as well as the diameter of the lower part of the plug housing, and in that step a) of drilling the bore comprises drilling the pencil until the said shoulder of the drill bit is positioned in abutment against the shoulder of the housing of the glow plug and the process being characterised in that step a) of drilling a bore is preceded by the installation of a centering pin at the orifice of the upper part of the plug housing for positioning one or more of the following elements: - a drill bit during the drilling operation of the pencil; - a tap during the threading of the bore; - an extractor while screwing it into the pencil thread. - a drill bit during the drilling operation of the pencil; - a tap during the threading of the bore; - an extractor while screwing it into the pencil thread.