HH21
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(Redirected from HH 21)
HH21, HH-21, HH 21, HH.21, may refer to:
- Piasecki HH-21, a variant of the Piasecki H-21 helicopter
- HH21, one of the Hamburger–Hamilton stages in chick development
- FLRT3, leucine-rich repeat transmembrane protein 3, also called "HH21"