These sizes refer to the ground joint on glass-on-glass pieces. The most common standard sizes are 10mm, 14mm, and 18mm — though 18mm is sometimes listed as 19mm. Both refer to the same actual measurement (18.8mm); it’s just rounded differently. As long as the sizing stays consistent, they’re interchangeable.
Stay flexible with the 14mm Female to 14mm Female Joint Adapter. This glass adapter connects two male pieces effortlessly — sold in a 5-pack for reliable, ready-to-use sessions.