9 and 20 Series TIG Back Caps and O-Rings: Replacement FAQ
By MIG/TIG/Stick Welders & Plasma Cutters | USA Weld – HTP ... | Published: 2026-11-02
Category: Product Reviews
Get clear answers on replacing 9 and 20 Series TIG torch back caps and o-rings, including length choices, leak fixes, and o-ring sizing limits.
Quick answer
For 9 and 20 Series torches, match the back cap length to your access needs and replace the o-ring whenever you swap caps or notice a leak. If you're unsure of the o-ring size, use the listed replacement o-ring for 9 and 20 Series back caps rather than guessing.
Why back cap length matters more than brand
Short, medium, and long back caps fit the same torch body but change how far the cap sticks out. A short cap helps in tight joints; a long cap gives more clearance for your fingers and tungsten adjustment. The trade-off is reach versus leverage—long caps can feel clumsy in confined spaces.
When a leak is the o-ring, not the cap
A back cap leaking TIG torch usually points to a worn or pinched o-ring, not a cracked cap. Inspect the o-ring for cuts or flattening before buying a new cap. If the cap threads are damaged, replace the cap; if the o-ring is damaged, replace the o-ring.
The o-ring size question
The catalog does not list a dash number or metric dimensions for this o-ring, so we can't confirm a generic size. Use the replacement o-ring specified for 9 and 20 Series back caps to avoid fit issues. If you need an exact size for a different source, measure the old o-ring with calipers and compare to the cap groove.
Replacement FAQ
- How do I choose between short, medium, and long back caps?
- Pick short for tight access, medium as a general-purpose default, and long when you want more finger room and tungsten adjustment clearance. The back cap set lets you try all three without committing to one length.
- Can I use a 9 Series back cap on a 20 Series torch?
- Yes—the listed back cap fits both 9 Series air-cooled and 20 Series water-cooled torches, including WP-9 and WP-20. Confirm your torch series before ordering, because other series use different threads.
- What causes a back cap leaking TIG torch?
- Most leaks come from a worn, cut, or misseated o-ring. Remove the cap, inspect the o-ring, and replace it if damaged. If the leak continues with a new o-ring, check the cap and torch body threads for damage. Replace the o-ring first—it's the cheapest and most common fix.
- How often should I replace the o-ring?
- Replace the o-ring whenever you install a new back cap, when you see cuts or flattening, or when a leak appears. Keeping a 3-pack on hand avoids downtime.
- What is the TIG torch o-ring size for 9 and 20 Series?
- The catalog does not publish a dash number or dimensions for this o-ring. Use the replacement o-ring listed for 9 and 20 Series back caps, or measure your old o-ring with calipers if sourcing elsewhere.
- Do I need a new back cap if the o-ring is bad?
- No—if only the o-ring is damaged, replace the o-ring. Replace the back cap if the threads are stripped, the cap is cracked, or it no longer seals with a fresh o-ring.
Product facts
- O-Ring for 9 & 20 Series TIG Torch Back Caps: O-ring for 9 and 20 Series TIG torch back caps, available in 3-packs. A 3-pack keeps spares on hand so a damaged o-ring doesn't stop you mid-project.
O-Ring for 9 & 20 Series TIG Torch Back Caps - Back Cap for 9 & 20 Series TIG Welding Torches: Back cap for 9 Series air-cooled and 20 Series water-cooled torches, including Weldcraft WP-9 and WP-20; short, medium, and long lengths plus a set. Choosing the right length and cap style lets you match access needs without buying a whole new torch.
Back Cap for 9 & 20 Series TIG Welding Torches
