Abstract: In a bolt welding gun, a tubular bolt holder is positioned on the front end of the gun body and is threadedly connected to the tubular front part of a slide-in unit. The position of the bold holder is axially displaceable relative to the front part. A nut is threaded onto the bolt holder for fixing the position of the holder with relation to the front part. In addition, a base ring is mounted on the front end of the gun body and supporting legs for the gun extend outwardly from the ring. The base ring is coaxial with the nut and has a recess into which the nut fits for preventing its rotation. A releaseable lock within the gun body is engageable with the base ring and prevents its rotation and, as a result, the ring holds the nut against axial displacement for securing the position of the bolt holder relative to the tubular front part.