Pololu - Aluminum Standoff for Raspberry Pi: 11mm Length, 6mm M2.5 Thread, M-F (4-Pack)

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.

Aluminum Standoff for Raspberry Pi: 18.6mm Length, 6mm M2.5 Thread, M-F (4-Pack) - Pololu

Black M2 M2.5 M3 M4 Aluminum Round Threaded Sleeve Standoff Pillar Connector Nut

Pololu 1942 - Aluminum Standoff: 1/2 Length, 2-56 Thread, M-F (4-Pack) - Kamami on-line store

Case - Melopero Electronics

M2/2.5/3/4/5/6 Aluminum Round Threaded Sleeve Standoff Pillar Long Nut Connector

Pololu - Aluminum standoff for Raspberry Pi

Stackable 0.100″ Female Header with Extra 0.3″ Spacer: 2x20-pin, Straight, POLOLU-2749

These 1/4-long hexagonal female-female aluminum standoffs keep parts spaced 0.25 inches (6.4 mm) apart. They are like elongated, 3/16″-wide hex nuts,

Aluminum Standoff: 1/4 Length, 4-40 Thread, F-F (4-Pack)

Pololu - Melopero Electronics

These hexagonal male-female aluminum standoffs keep parts spaced 1.0 (25 mm) apart and are great for building a multi-level robot chassis. Both ends

Aluminum Standoff: 1 Length, 4-40 Thread, M-F (4-Pack)

Aluminum Standoff for Raspberry Pi: 11mm Length, 4mm M2.5 Thread, MF (4-Pack) - Melopero Electronics