Pololu - Aluminum Standoff for Raspberry Pi: 11mm Length, 6mm M2.5

These hexagonal male-female aluminum standoffs are intended specifically for use with the Raspberry Pi. They keep parts spaced 11 mm apart, which is just the right height for mounting expansion boards with standard-size female headers, and they have 6mm-long M2.5 threads that are just the right size for the Raspberry Pi’s mounting holes. These standoffs are sold in packs of 4.

M2.5 Nylon Standoff Packs

Pololu - Male-Female Standoffs

Case - Melopero Electronics

These hexagonal male-female aluminum standoffs keep parts spaced 0.25 (6 mm) apart and are great for building a multi-level robot chassis. Both ends

Aluminum Standoff: 1/4 Length, 2-56 Thread, M-F (4-Pack)

Pololu 1942 - Aluminum Standoff: 1/2 Length, 2-56 Thread, M-F (4

Machine Hex Nut: M2.5 (25-pack) - Robot Gear Australia

Pololu 2082 - Aluminum Standoff: 1/4 Length, 2-56 Thread, F-F (4

Pololu 1971 - Nylon Spacer: 4mm Length, 4mm OD, 2.7mm ID (50-Pack

Pololu - Raspberry Pi Expansion Boards

Pololu A-Star 32U4 Robot Controller SV with Raspberry Pi Bridge

Pololu 2082 - Aluminum Standoff: 1/4 Length, 2-56 Thread, F-F (4

Pololu - Raspberry Pi Expansion Boards

Raspberry Pi Accessories - Standoffs