Concerning sizing of slides:
Do to bottle industry standards the cork end of all wine bottles in the USA are about American ring size, 8 1/4 to a tight fit for 8 1/2.
The cut end can vary in size. However, a straight neck will be smaller at the cut end as compared to a curved neck that widens to the bottle body. The wall thickness of the slide affects sustain and the sound in general. Thicker wall, more sustain but a heavier sound. Thinner wall a little less sustain but a lighter sound.

Concerning lengths: There are 2 lengths to consider. The total length including the lip and the playing length that does not include the lip.
I will cut a custom length for you. You may send metric measurements or inches, when I cut, no problem.

As a suggestion, You should measure from the web crotch of your finger to about the center of the slide finger fingerprint swirl on your finger tip pad.
This length will leave a little of the finger sticking out of the end of the slide to grip and control it naturally. But this is not a hard rule.

You can order any length that will conform to the type of bottleneck that you choose.

Ring Size:

METRIC      US RING SIZE
18.5 mm    8.5
19.5 mm    9.5
20.2 mm    10.5
20.5 mm    11.0
21.0 mm    11.5
21.5 mm    12
22 mm       13

A good idea is to send me the fretboard radius if you can, include the neck width at the nut and 12th fret.
Tell me you want. I will try to choose a slide for you. We don't buff out the seams, "micro-polish the surface", or anything like that. You simply play with the seams to each side.
We handcraft custom Wine Bottleneck Slides for slide guitarist, and will custom cut any length within reason.
Concerning the Photos of the slides on our website... The images have been resized to fit the required format. Some of the slides may look out of proportion. The photos are only to show you what the slides look like, and may not show the true dimensions...