A cable head for attaching a wireline to a downhole tool includes an upper tubular member and a lower tubular member removably attached by a threaded connection. The cable head includes a pack-off assembly disposed within the upper tubular member. The pack-off assembly includes a deformable pack-off element comprising an outer sidewall for sealing against an inner sidewall of the upper tubular member, and an inner sidewall for sealing around the wireline. The pack-off assembly includes a biasing means axially in line with the deformable pack-off element. The pack-off element and the biasing means are axially compressed between an internal shoulder of the upper tubular member and the lower tubular member when the upper and lower tubular members are removably attached by the threaded connection, to enhance the seal of the tubular pack-off element with the inner sidewall of the upper tubular member, and with the wireline.