These are hardware standards that I frequently reference:

Systems

• ISO 12100 Safety of Machinery, General principles for design, Risk assessment and risk reduction
• ISO 13849 Safety of Machinery, Safety-related parts of control systems
• VDI 2206 Design methodology for mechatronic systems

Mechcanical

• ASME Y14.1M-2012 Drawing sheet size and format
• ASME Y14.100-2017 Engineering drawing Practices
• ASME Y14.2 Line Conventions and Lettering
• ASME Y14.36M-2018 Surface Texture Symbols
• ASME Y14.41-2019 Digital product definition data practices ( model based definition )
• ASME Y14.5-2018 Dimensioning and tolerancing
• AWS A2.4 Symbols for welding
• IEC 60529-1989 Degrees of protection provided by enclosures (IP Code)
• ISO 286-1 Basis of tolerances, deviations and fits, shafts and bores

Electrical

• IPC-7251 Generic requirements for through-hole design

• IPC-7351 Generic requirements for surface mount design

• IPC-A-620 Requirements and acceptance for cable assemblies

• ASME-Y14.44 Schematic reference designators

  Refer to the linked page for the full list of designators and components.

  Designator	Component
  A	Assembly
  BT	Battery
  DS	Display
  J	Jack
  JP	Jumper
  K	Relay or Contactor
  LS	Loudspeaker
  M	Motor
  MK	Microphone
  P	Port
  PS	Power Supply
  S	Switch

• IEC-60757 Letter codes for designation of wire colours

  Wire Colour	Abbreviation
  BK	Black
  BU	Blue
  BN	Brown
  GN	Green
  GY	Grey
  OG	Orange
  PK	Pink
  RD	Red
  TQ	Turquoise
  VT	Violet
  WH	White
  YE	Yellow