Fjold,
I've found 3 different manufacturers of these extensions. Cheaperthandirt has one that sold last year for $5.00. This year it's $10.00 I trust everybody's getting 100% pay raises? This extension is worth about $.25....as a door stop or perhaps a chew toy for your dawg. The butt screws will pass right through the provided mounting holes....a real POS! Johnmasen.com has one for $14.95 which is a good one. The Cadillac is the Choate for about $20.00 available at Brownells as well as other gunsmith supply outlets. If you buy Cabela's make sure it's John Masen or better unless your looking for quality time with the pooch.
Mike