Enerflex (EFXT) had the best day in March 2021 by a mid-cap US stock on March 8, 2021, returning 61.5%.

ASSET	DATE	% RETURN
Enerflex (EFXT)	3/8/2021	61.52%
Aya Gold & Silver Inc Common Shares (AYA)	3/5/2021	56.98%
Edgewise Therapeutics (EWTX)	3/29/2021	37.89%
Upstart Holdings (UPST)	3/18/2021	37.77%
Red Cat (RCAT)	3/31/2021	29.44%
Upstart Holdings (UPST)	3/22/2021	28.87%
Nextdecade (NEXT)	3/29/2021	25.33%
Perpetua Resources (PPTA)	3/12/2021	21.16%
Definium Therapeutics (DFTX)	3/31/2021	20.26%
Quantum Computing (QUBT)	3/23/2021	19.48%
Pharvaris (PHVS)	3/15/2021	18.91%
Transocean (RIG)	3/10/2021	18.48%
Energy Fuels (UUUU)	3/15/2021	17.9%
RLX Technology (RLX)	3/29/2021	17.64%
Uranium Energy (UEC)	3/16/2021	17.45%
Uranium Energy (UEC)	3/12/2021	16.96%
Upstart Holdings (UPST)	3/25/2021	16.4%
CleanSpark (CLSK)	3/25/2021	16.06%
Upstart Holdings (UPST)	3/19/2021	16%
RLX Technology (RLX)	3/11/2021	15.69%
Nextdecade (NEXT)	3/24/2021	15.57%
Navios Maritime Partners LP Unit (NMM)	3/25/2021	15.46%
Aya Gold & Silver Inc Common Shares (AYA)	3/23/2021	15.33%
Magnite (MGNI)	3/17/2021	14.96%
Denison Mines (DNN)	3/2/2021	14.95%

Mid-cap stocks are treated as having a market cap between $2B and $10B.