For attaching an ion electrode or the like with a round electrode cap to the stand arm.
For 9615-10D/9618-10D/9681-10D/9680-10D/9600-10D/5002A-10C/8001-10C/8002-10C/8003-10C/8004-10C/8005-10C/8006-10C/8007-10C/8008-10C/8009-10C/8010-10C/8011-10C/1512A-10C/8201-10C/8202-10C/8203-10C