hard - helm
- hard alloy
- hard chromium plating
- hard disk
- hard facing
- hard glass
- hard lead
- hard magnetic material
- hard metal
- hard nickel plating
- hard porcelain
- hard rubber
- hard solder
- hard soldering
- hard steel
- hard water
- hard wood
- hardenability
- hardening
- hardening bath
- hardening furnace
- hardening steel
- hardening temperature
- hardness
- hardness of water
- hardness scale
- hardness test
- hardness tester
- hardware
- harmonic
- harmonic analyser
- harmonic analysis
- harmonic component
- harmonic drive
- harmonic motion
- harmonic oscillation
- harmonic oscillator
- harmonic resonance
- harmonic vibration
- harrow
- harvester
