The attachment that keeps the chaisaw straight and rides along the 2x6 is from Hud-Son. I saw them on Ebay, but bought it directly from them for around $40. It's well built, powder coated with sealed bearings.
I have no refrence to compair it to any other brand or type, but I have no problem recommending this one.
I had a $400 dollar Husqavarna chainsaw for about four years that died on me. I filled up a five gallong gas can with the fuel mix and never emptied that can. So I feel comfortable saying I didn't use it a whole lot. The repair shop said the motor didn't have any compression and was unrepairable. I won't buy another product from them again.
This time I decided to buy a cheaper chainsaw and liked the Poulan Pro. It's got a 20 inch bar and 46cc engine. Lots of power and starts much easier then thas Husquavarna piece of crap.
Here is the first cut.