Vapers need calipers folks. Almost every device out there comes with no specifications on size for any of its parts. For those that do list this information I commend them. There are parts that over the lifetime of a device will need to be replaced, this would be small screws, orings and of course tank tube sections. You can also use them to identify wire gauge size for those who might have a mix of wire that is unlabeled. Also by having calipers you can be sure your device is within that makers specification and that the device was properly designed for glass in the first place. Many devices are just not designed for glass. Over the years we have been able to help folks to get glass fit onto some of these devices and some just could not be supported. Some makers design strictly for Metal and Plastic tank sections My advice is if you want to use glass dont buy those devices, if glass is not important then it doesnt matter but folks should be aware of this and hopefully before they spend a lot of money on a device. Inexpensive digital calipers are available from Harbor Freight and other online sources for around $20 and they are surprisingly accurate. We suggest not getting the all plastic ones as they can easily deform giving false measurements, all of the ones we have used that have a metal slide and tangs though have been very close to our high end and much more expensive calipers. Please note that you should not try to measure the length of a battery using metal calipers as this would short the battery. A device that seals on the ID (internal diameter) of the tank tube needs to have any metal part that goes inside of the tube sized a minimum of 0.25mm under the nominal glass ID. Nominal is the perfect world size something would be if there was no such thing as tolerance specifications. A tank with a 19mm ID should have no part that must go inside of the glass over 18.75mm for example. We recently had one order of custom cut glass that did not fit, the customer had calipers and noted the glass was 0.20mm under size from nominal. The device he was trying to fit measured at just 0.05mm under the nominal ID of that glass. This particular device ships with a plastic tank so the maker of that device is certainly within their own design specification because they do not design for glass. We refunded this customer even though it was a custom order as we had not explained that glass production is not as precise as machining even from the best manufacturers. We have noted this information about tolerance on the custom cut to length pages now and from here on out it will be up to the customer to make sure their device is properly designed to use glass on it. We are always happy to help manufacturers or customers in designing or measuring devices to access the fitting of glass, just ask. Got Calipers?