These are Du-Bro's "Permanent Mount" 2-56 Blind Nuts.

Features

Zinc plated, metal construction.
Ideal for mounting engines, landing gear, cowls, hatches, etc.
The perfect mounting nut for hard to reach areas.

Includes

(4) Blind Nuts

Requires

Drilling a 3.2mm hole to install

Specifications

Diameter: 6.8mm OD of flange
Length: 3.9mm
Thread Size: 2-56