4710807 | Rubber Plug for Lab 5, 10 & 20 (2.125" OD)

Replacement Plug, 2.125" OD with 2" ID center hole. 

Not sure when your dewar was manufactured? You can decipher the following information from your Chart MVE Serial Number.

Sample Serial Number
NPB2011012046

This serial number has 5 distinct sections:

NP B20 11 01 0546

NP - is the site of manufacture. Example 'NP' means New Prague, MN 56071
B20 - is the same constant internal MVE code.
11 - is the year of manufacture.
01 - is the week of manufacture. Example '01' means the first week of the year.
0546 - is the number that vessel was in production for that week.