We're planning to measure non invasive blood pressure in C57 mice. Weight should be around 20-40 Grams.

There are 2 sizes available at Kent Scientiffic: small and extra-small... they're both supposed to be for 8-75 grams.

Any suggestion which one should I buy?

The company says C57 teng to have small tails... but we'll be doing serial measurements up to 1-2 years old.

https://www.kentscientific.com/products/default.asp?CategoryId=289&Mouse_Rat=CODA+Accessories

Thanks in advance