LAB - Glassware Joint Sizing Guide

Glassware aparatus for the laboratroy requires various joints to be made between pieces of glassware. These temporary joints need to be leak-proof and at times create a closed pressurised system. The joints can be sealed and held together using grease, sleeves and clamps/clips.

There is a sytem of joint sizing that uses a two-number code (e.g., 24/40) where the first number is the widest outer diameter (OD) in mm, and the second is the nominal joint length in mm; sizes vary by region (US ASTM vs. European ISO), but the taper (usually 1:10) is standard, meaning the diameter decreases consistently along the length, allowing some interchangeability, but exact diameter and length must match for a perfect fit, with common sizes like 14/20 (US) and 24/29 (ISO).

'A' and 'B' length tapered joints refer to the dimensions of standard ground glass joints where 'A' is the nominal OD and 'B' is the length of the ground section (e.g., 10/18 means A=10mm, B=18mm).

A vs. B Length:

• A-Length (Standard/Shorter): Often shorter, like 19/22 or 24/40, offering a shallower connection.
• B-Length (Longer): Longer versions for the same diameter, such as 19/26 or 19/38, providing a deeper, more secure connection.

Examples:

• 19/22 (A-length): 19mm wide at the top, 22mm long.
• 19/26 (B-length): 19mm wide at the top, 26mm long, making it a longer version of the 19mm joint.
• 24/40 (A-length): A common, longer standard, 24mm wide, 40mm long.

In essence, if you need a longer ground joint for a specific diameter, you'd look for the 'B' length (like 19/26) instead of the shorter 'A' length (like 19/22).

Here is a useful video to explain further about joint sizing and also creating leak-proof joins in your laboratory glassware.

ProSciTech's collection of glassware joint fittings and adapters