The contents of the spares kit are used to service and maintain your optical cryostat to ensure optimal performance. Contents of kit: 8 SCREW NYLON CHSE M03.0 X 004, 2 SCREW A4ST CAP M03.0 X 006 SET, 4 SCREW A4ST CAP M04.0 X 010 SET, 5 O RING R02137 BS028 NBR 70 SH, 1 O RING R03200 BS136 NBR 70 SH, 1 BOX PLASTIC P 3.0X2.0