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What is Mil-Spec?

Working with a variety of different clients in the aerospace and military industries, we receive a wide range of purchase orders that need to be documented and relayed to our team hastily. To ensure that the specifications of these jobs are presented clearly, customers will use “specs” to communicate what they are expecting out of their purchase order. These specs are consistent throughout the industry and are used to quickly relay type, class, and other information to our team members.

Why are Mil-Specs Important?

Mil-Specs (short for Military Specs) are common practice when working with the aerospace and defense industries. Since both industries work with aircraft, there is a thin margin of error for their manufacturers. To prevent process error, The Department of Defense develops military specs for all their manufacturers and contractors to follow.

 It only takes one misstep in the metal finishing process to derail an entire multi-industry manufacturing process. AOTCO is dedicated to keeping our highly trained staff informed on the latest mil-spec requirements.


Mil-A-8625 is one of the most used military specs for anodizing. The spec defines 6 types and 2 classes. Type is used to determine what type of anodize will be used (Chromic, Sulfuric, Hard Coat) and Class represents whether the anodize is dyed or not.

Types of Anodic Coatings Available

Type 1 – Conventional coatings produced from chromic acid bath.

Purpose: Delivers an electrically non-conductive surface with improved scratch and corrosion resistance. Primarily used in aerospace applications and on castings where components that may undergo flexing due to heat changes or mechanical means.

Type 2 – Sulfuric acid anodizing, conventional coatings produced from sulfuric acid bath.

Purpose: Intended to improve surface corrosion protection under severe service conditions or as a base for paint systems

Type 2B – Thin sulfuric acid anodizing, for use as non-chromate alternative for Type 1 and 1B coatings

Purpose: Non-chromate alternative to Type 1 and 1B coatings, where corrosion resistance, paint adhesion, and fatigue resistance are all required

Type 3 – Hard Anodic Coatings

Purpose: Provide wear and abrasion resistant surfaces with improved corrosion protection due to greater thickness and weight than the conventional anodic coatings. Reminder: Sealing of Type 3 coatings is not recommended unless corrosion resistance is also a factor, as both wear resistance and fatigue strength can be reduced by sealing

Why Use Hard Anodize?

Hard Coat Anodize (or Type III) provides a thicker layer of protection than standard sulfuric or chromic processes. This thicker layer provides increased abrasion resistance as well as a higher resistance to corrosion. Due to these qualities hard coat anodize provides a longer lasting and more aesthetically pleasing finish than other anodizing finishes. Hard Coat anodize is commonly used with parts that require heavy use or wear resistance. Components like pistons, hydraulics, machine exteriors, and kitchenware all benefit greatly from the addition of hard coat anodize.

Types of Anodic Coatings NOT Offered

Type 1B – Chromic acid anodizing, low voltage process

Type 1C – non-chromic acid anodizing, for use as non-chromate alternative for Type 1 and 1B coating


Class 1 – Non-dyed

Class 2 – Dyed