Apparatus (10) for transmission testing of a telecommunications jack (100) having a plurality of insulation displacement contacts (IDCs) (103), the apparatus (10) including: a base (30); a plurality of transmission test probes (31) associated with the base (30); and a jack holder (20) for removably coupling the jack (100) to the base (30) such that IDCs (103) of the jack (100) are in electrical communication with corresponding test probes (31); wherein the jack holder (20) is fixed relative to the base (30) during testing, such that the jack (100) remains stationary with respect to the probes (31).