Ive been looking around for a 3 lug adapter to put on the end of my barrel, but i cant find hardly any information about them. If any of you guys/gals can help answer my questions, i'd be greatly appreciative.

Where can I find decent ones? (i spent a few hours on google and found all of one place that even sold them)
How much threaded area do they usually need to have to work? (ive got a barrel with a front site on it and would rather like to avoid moving the site if i can get away with it.)
How would you go about permanently attaching it to the barrel?

If it helps to explain the project, here goes: I'm going to be mounting a 3 lug adapter on a Marlin 1894C in .357 mag to attach a SWR Trident 9 to it. I want to go with the 3 lug so that I don't have to worry about any threads loosening up during firing, and don't have to worry about over tightening it trying to prevent threads from loosening up during firing.

Use rockset to permatach that 3 lug on and 1/2 inch of barrel will be enough for threads.
I have used a few of these 3 lug adapters and never had a problem.
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Adapters on the bottom left

3-lug adapters - $50





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The replies were very helpful. Thanks Much

That's going to be a pimp marlin.

Gemtech makes one, too.  They 3 lugged a gun for me.