Globe Scientific 116152W Polyethylene Flange Plug Cap for Test Tubes, 16mm Size, White (Pack of 1000): Science Lab Cap Plugs: Amazon.com: Industrial & Scientific
Flange Plug 2 ' (60mm) 150 # Carbon Steel A105n with Threaded Pipe Plug - China Hex Head Plug, NPT Plug | Made-in-China.com
Globe Scientific 118240K Polyethylene Flange Plug Cap for Test Tubes, 13mm Size, Black (Pack of 1000): Science Lab Cap Plugs: Amazon.com: Industrial & Scientific