Abstract: A universal electrode holder having a holder body including a top face, a bottom face, perpendicular sidewalls and end walls, wherein one side wall is stepped to define offset lower and upper surface portions joined by a horizontally disposed connecting surface portion; a reference plate having a reference surface disposed to extend transversely of the lower and connecting surface portions; an indexing plate having an indexing surface and being slidably mounted on the lower and connecting surface portions to selectively vary the distance between the reference and indexing surfaces; a clamp device fixed to the holder body for releasably clamping an electrode of rectangular cross section in a mounted position, wherein its opposite edge surfaces engage with the reference and indexing surfaces, its upper and rear side surfaces engage with the connecting and lower surface portions and its front side surface engages with the clamping device; mounting and aligning means including a plurality of ribs depending from t