a sewing machine is provided for splicing together two different threads . the machine includes a thread tree with a number of thread spools with each thread thereof being inserted through flexible plastic tubing . a movable carriage assembly locates the new thread to be spliced relative to a splicing device passageway that receives the new thread to be spliced along with the old thread . the splicing device includes a front air inlet for drawing the new thread into the passageway of the splicing device and a rear air inlet for creating air turbulence during the splicing operation . also used in moving the new thread through the passageway is an insertion drive roller connected to a pivotal rocker . a thread clamp cover connected to the rocker cooperates with the trimmer blades to trim the old thread . a thread clamp and a thread clamp magnet cooperate to hold the old thread in a desired position during the insertion of the new thread into the splicing device . a tensioning assembly is able to adjust new thread tension based on a desired tension for the new thread .