OPTI-GUARD sets the standard for low-impact, easy to use pre-column protection. Designed for use with analytical (4.6 mm, 3.0 mm I.D.) and narrow bore (2.1 mm, 1.0 mm) columns, the patented floating stem design automatically adjusts to any manufactures tube stop depth for a zero-dead volume connection every time. The OPTI-GUARD 1 mm requires no special connecting hardware or tools for installation.. Particle Size: 40 µm. Matrix active group: Cyano phase. Pack of 5. . . Sigma-Aldrich 51179-U OPTI-GUARD Guard Column, 1mm, Pack of 5. Country of Origin : United States. Part Number : 1179R60PK. Pack of : 5.