The present invention relates to an adapter (1) for a coaxial connector assembly (2) comprising a tubular outer conductor (3) and a pin-shaped inner conductor (4) both extending in a mounted position in a longitudinal direction (z) and a spacer (5) which in the mounted position is arranged inside the outer conductor (3) encompassing the inner conductor (4) at least partially and by which the inner conductor (4) is positioned with respect to the outer conductor (3). The spacer (5) comprises a first half (5a) and a second half (5b) which are interconnectable to each other along a separation plane extending in the longitudinal direction (z), wherein the first and/or the second half (5a, 5b) comprise at least one holding means (6) to hold the inner conductor (4) in the mounted position.