Details of extruder for Smart Core

The BOM for the SmartRap Core doesn't mention anything about parts for the extruder. The assembly video from Smartfriendz shows that I will need a bearing, screws, and a hobbed bolt. Does anyone know where I can details on what size bearing, bolt, and screws I'll need?

A hobbed bolt is for a wades extruder and the SmartRapCore typically uses a Bowden extruder which does not require a hobbed bolt.

I went with this extruder instead of the one from SmartFriendz. I could not get enough force on the filament with the one from SmartFriendz. This one works really well: BOM is listed in the article.
[www.thingiverse.com]

The default SmartRapCore extruder is based on the simple extruder. The BOM is listed in the article.
[www.thingiverse.com]

Thank you! That was exactly the sort of information I was looking for. I'll start with the simple extruder and hope it works well enough for me to print the parts for a better one.

The airtripper is indeed a good extruder. I love it with the MK8 gear to drive the filament.

I tried the smartrap one and didn't like it - not enough give in it to apply even pressure (had a slightly off-centred Mk7 gear). Got this one now - chose it because it uses minimum material and hardware. I use a Mk8 gear now and motor has completely stopped missing steps. I use a spring and slighly longer tensioning bolt to accommodate it, unlike the photo on thingiverse:

http://www.thingiverse.com/thing:275593

I had the same problems with the SmartrapCore extruder. My Ultimaker broke a tooth in the middle of an important print. What to do in a hurry? I took the extruder from my small SmallrapCore and finished the print. Success, customer got his print. Then I printed two new extruders to be used on the small printer and the new UltimakerCoreXY using the same gcode as for the first extruder I made. So far so good, but...

None of the new extruders was working. I fiddled with all the parameters for the steppers, power, steps/rotation but I couldn't get a reliable motion of the filament.

So my preffered extruder right now is [www.thingiverse.com]

I have been pretty happy with the SmartRap Core extruder so far, but then I have been printing for all of 5 days. What would the symptoms be of an inconsistent feed rate? Varying line thickness? I am definitely going to print one of the others just to give it a try.