The ACU is the Army Combat Uniform, the digitally camouflaged multi-purpose combat and work uniform of the Army. The ACU replaced the previous woodland camouflaged Battle Dress Uniform, or BDU. Part of the ACU is the patrol cap, a cover that must be worn outdoors. Rank displayed on the patrol cap is sewn into the cap. The ACUs use hook-and-loop attachments to secure additional uniform items such as unit patches, rank, skill tabs and recognition devices.
Purchase appropriate rank insignia to match your personal rank, either from the local base exchange or off the Internet.
Pin the insignia above the bill and below the top of your patrol cap with the straight pins. Make sure the insignia is centered.
Sew the insignia on the cap with matching needle and thread, stitching from the inside of the cap to the back of the insignia so the thread does not show. Remove the straight pins when you are done sewing.