After searching high and low I finally got the12v trigger relay plug size from optoma for the HD72, and just wanted a permanent record here:

Outside Dimension: 4.00mm
Inside Dimension: 1.7mm

Radio Shack part # 273-1705 will work.

My bad - I just found out this is the size plug for the HD70. The dude from Optoma sent me the wrong specs. I'm trying to get the right specs now. They may be the same for all Optoma projectors, but stay tuned...

Ok it works. The HD70 and the HD72 have the same size plug. It's the Radio Shack AdaptaPlug "B"

Hopefully this helps someone out there since it took me forever to find it. ;-)

After searching high and low I finally got the12v trigger relay plug size from optoma for the HD72, and just wanted a permanent record here:

Outside Dimension: 4.00mm
Inside Dimension: 1.7mm

Radio Shack part # 273-1705 will work.

Thanks for posting this, I agree this should be on permanent record. We tried Radio Shack part #274-1532, which has same dimensions, except it is solder-type, not adaptaplug. It seemed too small, so we used this part number instead: 274-1567. Fits much better, doesn't wiggle too much in the 12v trigger jack of the Optoma HD72.

Here are all 3 part descriptions from Radio Shack:
1. 274-1567 <<<seems to fit the best
Size K Coaxial DC Power Plug (2-Pack)
* Replaces damaged power jacks
* Tip size: 5mm O.D.x2.1mm I.D.
* Solder type
http://www.radioshack.com/product/index.jsp?productId=2103612

2. 274-1532
4.0x1.7mm Coaxial DC Power Plug (2-Pack), aka Size B Coaxial DC Power Plug
* Tip size: 4.0x1.7mm
* Barrel length: 22.8±1.0mm
* Solder terminal
http://www.radioshack.com/product/index.jsp?productId=2102598

3. 273-1705
Adaptaplug B, aka Size B Adaptaplug
Adaptaplug B conversion size: O.D.: 4.0mm. I.D.: 1.7mm
http://www.radioshack.com/product/index.jsp?productId=2062424

FYI, wikipedia article on coaxial power connectors: http://en.wikipedia.org/wiki/Coaxial_power_connector

Also, Optoma's FAQ states:
"Q49. What is the appropriate connector for the 12 v screen trigger?
A49. Size: H Coaxial, DC PowerPlug; Tip size: 3.5 mm OD X 1.3 mm ID (e.g., Radio Shack Part #274-1571)"
http://www.optomausa.com/FAQ_detail.asp?offset=40&FAQ_id=49

But for the Optoma HD72, the information provided is not correct (too small). Perhaps I have misread the FAQ?