Standoffs can be many shapes and sizes and made of many different materials. those are made of metal. Insulating standoffs keep two parts from touching each other, thereby preventing an electronic short. Cable thumbscrews are often screwed into standoffs on the back of computers. Standoff sizes are usually measured by the Unified Thread Standard. Size 4-40 is used to secure cables to external computer ports and size 6-32 is used for motherboard mounts.  those are good for Arduino raspberry pi and electronic PCB separation and Smart Car Robot Kit.

Cite pillars column M3 30 +6 30 +6 means: 
M3 is the circular threaded portion of a diameter of 3 mm, 30 +6 refers to the length of the threaded portion of 6mm, the hexagonal column section length of 30mm, the total length of 36mm
 
Shipping list:                                                                                                                                        
3 * 8 through pillars       16 
 15 +6 pillars                  20 
 20 +6 pillars                  10 
 40 +6 Tongzhu in          10 
 M3 nut                          60