The #6 rubber stopper is roughly 25mm (1) tall, only $0.80 for one with discounts for volume and is included with the following glassware in
Rubber Bung Stopper with Hole for Airlock for Fermentation
Rubber Stoppers 1 inch
Home Brew Ohio #6 Drilled Rubber Stopper Set of 3
Rubber stopper size 6 no Hole 1-1/8 top diameter 1-1/16 bottom diameter
Rubber Stopper- Size 6- Solid
259100-6 - Laboratory Grade Rubber Stoppers, Green Neoprene Rubber, Size #6, 32 x 26 x 25mm, 19 per Package
Item Package Height:2.54 Centimeters Country Of Origin: United States Hole For Airlock (Not Included) Product Type: Mechanical Components
Rubber Stopper- Size 6- Drilled
Drilled Gum Stopper #6 1/2 – Grains & Taps
Rubber test-tube stopper Includes 1 lb. of stoppers
GSC International RS-6 Rubber Stoppers, Size 6, Solid (1-Pound Pack), Black
6 Drilled Rubber Stopper (DRS) – Wine and Hop Shop
Chemglass - CG-3027-05 - Rubber Stopper, #2, One Hole, Black