How to Choose a Pyrex Cup Kit for Your TIG Torch

By MIG/TIG/Stick Welders & Plasma Cutters | USA Weld – HTP ... | Published: 2026-10-16

Category: Buying Guides

Pick the right Pyrex cup kit by matching your torch series and cup size, and learn what each kit includes so you can see the arc without downtime.

Quick answer

Choose a Pyrex cup kit by matching it to your torch series first, then to the cup size you actually weld with. If you run a 17, 18, or 26 series torch and want a clear tig glass cup in a #12 size with spare diffusers and o-rings, the FUPA12 Pyrex Cup Kit is the practical pick. If you need standard sizes for 17/26 air-cooled or 18 water-cooled torches, the Standard Pyrex Cup Kit covers that. If tight access is your problem, a 1/16" stubby gas lens kit lets you run smaller 9/20 series alumina cups on the same torch.

Match the kit to your torch series before anything else

Pyrex cup torch fitment starts with the torch series, not the cup size. A kit built for a 17 series torch will not thread onto a 9 series torch without an adapter, and the gas lens or collet body inside the kit is sized for that specific torch body. Before you compare prices or cup diameters, confirm whether you are running a 17, 18, 26, or 9/20 series torch. If you are unsure, check the torch body stamping or the consumables you already own — the collet size and cup thread are the fastest tells.

Decide what you need the clear tig cup to do

A clear tig cup earns its place in two situations: when you need to see the arc and puddle in a joint you cannot easily reposition, and when you are teaching or learning and want visual feedback. Pyrex cups give you that visibility, but they trade away some durability compared to alumina. If your work is mostly flat, high-amperage, and repetitive, a standard ceramic cup is cheaper and tougher. If you are doing tube joints, thin stainless, or any fit-up where you are welding by feel, the visibility is worth the care Pyrex demands.

Size the cup to the joint, not to the kit

Pyrex cup sizes follow the same numbering as alumina cups, so a #12 is a large cup and a #6 is small. Large cups spread shielding gas over a wider area, which suits stainless and titanium where coverage matters, but they are harder to fit into corners and they consume more gas. Small cups concentrate the gas and reach into tight spots, but they offer less coverage on dirty or drafty work. Buy the size you already weld with most, then add one size up or down only if you have a specific joint that demands it.

Count the spares before you buy

The hidden cost in any tig cup kit buying guide is downtime. O-rings and diffusers wear or get lost, and a kit that includes spares keeps you welding instead of waiting on a single replacement part. When you compare kits, look at what is in the box beyond the cup itself: diffusers, o-rings, collets, and gas lens bodies all matter. A kit with one spare diffuser and three spare o-rings is a better value than a cheaper kit that leaves you ordering a $4 part and paying shipping twice.

Decision rules for buying a Pyrex cup kit

If you run a 17, 18, or 26 series torch and want one size done right: Buy the FUPA12 kit when #12 is your working size. It ships with two cups, diffusers, a spare diffuser, and three spare o-rings, so you are covered for the wear parts that fail first. Best when you already know #12 fits your joints and you want spares on the shelf.
If you need flexibility across sizes on a common torch: Choose the Standard Pyrex Cup Kit for 17/26 air-cooled or 18 water-cooled torches and select the size option that matches your most common joint. Buy a second size later only when a specific job demands it. Best when your work varies and you do not want to commit to a single cup size.
If the joint is too tight for a full-size Pyrex cup: Use the 1/16" Stubby Gas Lens Kit to run 9/20 series alumina cups on your 17, 18, or 26 torch. It shortens the torch head for access, but you give up the clear cup visibility. Best for restricted access where fit matters more than seeing the arc.
If you weld high-amperage, flat, repetitive work: Skip Pyrex and stay with alumina cups. Pyrex is for visibility, not for abuse, and the cost per cup is higher when you break one. Do not buy Pyrex just because it looks better in photos.

Kits worth comparing

FUPA12 Pyrex Cup Kit, #FUPA12: FUPA12 Pyrex Cup Kit includes two #12 flared Pyrex cups with diffusers, one spare diffuser, and three spare o-rings. You get a complete #12 setup plus spares, so a lost o-ring or worn diffuser does not stop your work.
Pyrex Cup Kit, Standard: Standard Pyrex Cup Kit fits 17 and 26 series air-cooled torches and 18 series water-cooled torches, and is available in multiple sizes. If you run a common 17/18/26 torch, this kit lets you pick the cup size that matches your joint instead of committing to one size.
1/16" Stubby Gas Lens Kit f/17, 18, & 26 Series TIG Torches: 1/16" Stubby Gas Lens Kit lets you put a 9/20 series alumina cup onto any 17, 18, or 26 series TIG torch, and includes a 1/16" collet, gas lens collet body, #6 alumina cup, heat shield, and medium back cap. This shortens the torch head for tight access, which is the right move when a full-size Pyrex cup will not fit the joint.

Who each kit fits

Best for

Welders running a 17, 18, or 26 series torch who want a clear tig glass cup in a known size
Anyone doing tube, stainless, or thin-gauge work where seeing the puddle matters
Buyers who want spare diffusers and o-rings in the box to avoid downtime

Not for

Welders on 9 or 20 series torches without checking adapter requirements
High-amperage production work where alumina cups are more economical
Anyone who has not confirmed their torch series and existing cup size