An adapter is configured to hold a loose tube fiber cable and is mountable into a fusion splicer. The adapter includes a clamp base having a first and second grooves, each groove having a centerline, a width and a depth. The depth of the second groove is greater than the depth of the first groove, such that a shoulder is formed between the first and second grooves. The centerlines of the grooves align. This allows for the loose tube fiber cable or splice-on connector to be properly positioned within the grooves. The first groove is V-shaped. The second groove may be V-shaped, U-shaped or square-shaped. A clamp cover seats on the clamp base. The clamp cover has a compressible pad which, when the clamp cover is placed into a facing relationship with the clamp base, the pad aligns with the first groove.