Previously to blow bulbs in glass, I used a crude jig that sealed poorly and was suitable for only one size of tubing. To improve on this, I made a universal blow hose. One end has a cleanable mouthpiece (the hose itself tends to collect dust) and the other has an airtight swivel containing a sealed ball bearing. Both are made of Delrin. The swivel has a 1/4 inch outlet on either end, allowing the hose to be connected to a rubber stopper of any size. It works very well, and the thickness of the silicone rubber hose allows it to be used unsupported without the risk of twists or kinks. I have found that rubber stoppers are quite durable, and can be used in close proximity to the heat of a torch. The piece of glass (3/4 inch Pyrex) pictured above was heated and blown just beyond where it was cut on the right side.