These are Du-Bro's "Permanent Mount" 4-40 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 4mm hole to install

Specifications

Diameter: 8mm OD of flange
Length: 4mm
Thread Size: 4-40