Improvac Venous Blood Collection Tube Serum Tube Clot Activator / Separator Gel Additive 16 X 100 mm 8.5 mLGold Plug Seal Cap Polyethylene Terephthalate (PET) Tube. Features: IMPROVAC® Gel and Clot Activator Tubes offers serum for determinations in chemistry and serology; The tube contains a gel that forms a stable barrier between the serum and the cellular components of the whole blood after centrifugation; They are coated with silicone and micronized silica particles to accelerate clotting. Packaging: 50ea/bx, 20bx/cs (1000ea/cs)