Galvanized plugs, Dnipropetrovsk region.

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A plug is an element of the completion of an air duct or another part that stands at the end of the ventilation system.
The cap ensures the tightness of the ventilation system, maintains the set pressure and air temperature, and also protects the system from dust, moisture and foreign objects getting inside.
Plugs are round and rectangular.(//tractor-service.com)
Plugs must be made of the same steel from which the ducts of the entire ventilation network are made.
The cross-sectional dimensions of the plug must completely coincide with the cross-sectional dimensions of the duct on which it is installed.

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