Acceptable vs. non-acceptable consumable wear - retaining caps
All consumable sets contain two retaining caps—an inner cap and an outer cap. The inner retaining cap holds the nozzle and swirl ring, both covered in earlier posts, in place while directing coolant flow to the exterior of the nozzle. All inner caps have a composite ring which is designed to mount the shield concentric to the nozzle orifice, and route secondary gas to the shield.
The size of this ring varies depending on your amperage level. The picture at the top of this post shows the inner cap from a 130 amp system on the left and a 260 amp system on the right. You can see how the composite ring on the 130 amp cap is much smaller than the ring on the 260 amp cap.
No matter the size of your ring, you’ll want to inspect it closely to be sure it is perfectly round with a smooth surface. In addition, you want to be sure the ring is not burned or cracked, and that the small holes found just under the top edge aren’t plugged up with metal spatter, grease, or other debris. Some inner caps also have bleed holes at the base. If your cap has these holes, you’ll want to inspect those as well. 
Moving on to the outer cap, its function is to hold the shield in place over the inner retaining cap, and direct your shield gas to the shield. The outer cap also has a contact tab that is used on some torch height controls (THC) as an ohmic or electrical contact to the plate.
When inspecting the outer cap, there are two things you want to look at. The first is the top opening, which needs to be perfectly round with no nicks or arc marks. The second thing are the threads at the base of the cap. You’ll want to be sure these threads are clean and not worn out. 
You can help prolong the life of your outer cap by occasionally taking a Scotchbrite pad to it. The pad is helpful for removing spatter off the front. The other thing you can do is spray a water-based MIG welding anti-spatter spray on the front of the cap. You might remember this same tip from our post on the shield.
Provided you take good care of both, your inner and outer retaining caps should last you a very long time. The change-out ratio compared to an electrode is as high as 100 to 1. Meaning, you’ll go through 100 electrodes before needing to change even one inner or outer cap. The secret though is to keep your caps very clean, especially the composite ring on the inner cap, as even a tiny bit of dirt or grease can cause carbon tracking or burning.
That concludes our series of posts on "Acceptable vs. non-consumable consumable wear." To recap, we've covered six different consumables in five posts:
1) Electrode 2) Nozzle 3) Swirl ring 4) Shield 5) Inner and outer retaining caps
Which post was your favorite?