Thread tension device for sewing machine

A sewing machine comprising:

• a thread tension device which is capable of adjusting a tension of a needle thread by an adjusting tool having a distal end, the thread tension device comprising:
• a thread tension mechanism including:
• a pair of thread tension discs holding the needle thread therebetween;
• a thread tension spring biasing one of the thread tension discs toward the other and having two ends;
• a thread tension dial adjusting a tension exerted on the needle thread by the thread tension discs subjected to a spring force of the thread tension spring;
• a spring force adjusting cam which is formed in the thread tension dial and is capable of adjusting the spring force of the thread tension spring;
• a transfer plate following the spring force adjusting cam so as to be capable of adjusting the spring force of the thread tension spring;
• and
• a first adjusting member which is threadingly engaged with the transfer plate to receive one end of the thread tension spring;
• a thread guide assembly provided with the thread tension mechanism, thread guide assembly having a through hole formed therethrough so that the adjusting tool is externally insertable into the through hole;
• and
• a second adjusting member rotatably mounted on the transfer plate and engageable with the distal end of the adjusting tool inserted into the through hole so as to be rotatable with the adjusting tool, thereby rotating the first adjusting member by rotation of the adjusting tool;
• an arm in which the thread tension device is provided, the arm having an end;
• a pillar connected to the end side of the arm;
• a head provided at a side of the arm opposed to the pillar;
• an exterior cover covering the arm and at least a part of the pillar;
• and
• a face plate detachably attachable to the head so as to be capable of accommodating the head, the face plate having a face opposed to the thread tension mechanism of the thread guide assembly formed with the through hole, said face being exposed when the face plate has been detached from the head.