http://www.camerafilters.com/pages/spacerrings.aspx

I'm not sure if this has been posted before, but this website sells lens spacer rings with a variety of thread sizes, in lengths of 1 inch or 1.5 inches. These tubes are less than half the cost of the Thorlabs tubes that many have been using, and may be a working alternative to the overpriced optical component that we know and love.

"Spacer Rings - High quality black metal spacer rings. Male threads on one side and female threads on the other. This ring is used to increase the distance of the accessory from the camera lens.

These rings can be used with camera filters, extension lenses, lens hoods, and additional spacer rings."

Prices are as follows

1 Inch Tube:
49mm - $4.21
52mm - $5.21
55mm - $6.21
58mm - $7.21

1.5 Inch Tube:
49mm - $4.41
52mm - $5.41
55mm - $6.41
58mm - $7.41

According to the website, they're only available in the US.

Now, the only concern is whether or not the 52mm tubes have an inner diameter of 2 inches. I'm emailing them now to find out. If so, then this could be pretty helpful to us DIYers.

My apologies if this has been brought up before a long time ago. I tried searching but didn't find anything about them.

I talked to the guy running the place on the phone. When I called him he got up and measured the ID for me. He said the 52mm have an ID of about 48.5 mm, which is too small for us, so I ordered the 55mm tubes, which have an ID of slightly larger than 2 inches. I'm going to take some thin plastic and make a shim that I can use to close the gap.

http://search.stores.ebay.com/ASIAN-CAMERA-LLC_Spacer-Ring_W0QQfciZQ2d1QQfsnZASIANQ20CAMERAQ20LLCQQsaselZ103166399QQsofpZ0

Shipping is lightning fast.

yeah I just bought one from asian camera. Ordered it after ordering all my other 35mm adapter parts but got it first (about 2 business days). I ordered stuff from camerafilters.com too, but for oscillating adapters, 58mm probably isnt enough. I went for the 62mm tube.

I'm willing to be the ID would be able to fit a 49mm ring inside. The thorlabs did anyway.

I ordered the 58. Going to get ahold of Jetset tonight to order a Vibrating holder.