The SAK CS:R Center Foot

Mechanical Parts

There are several parts that you will need to complete the Center Foot Assembly.
updated 04/30/19

Caster Version
Colson Caster 1 Series Threaded Swivel Stem Caster
with a Performa Rubber (Flat/Grey) 3 in wheel
Part # 1.03054.441 MTG55 Note:  3/8-16  1.25 in stem
I bought mine on eBay from :
search for "Colson Swivel Stem Caster with 3" Performa TPE Gray Non-Marking Wheel"
they take best offers for 10-15% less, particularly if also buying wheels for the outer feet
at the same time (also combines shipping)

ServoCity Omni Wheel Version
ServoCity Parts
ServoCity 4 in Omni Wheel - Single Wheel
595671 - $9.99 - need 8 wheels
FR6ZZ bearing 3/8" ID x 7/8" OD Flanged Ball Bearing (2 pack)
535048 - $3.29 for 2 bearings - need total 8 bearings ($1.65/bearing  + shipping - order same time as wheels!)
ebay Bearing supplier (alternate supplier)
search for FR4ZZ-FR6ZZ-FR8ZZ-MR4-MR6-MR8-Series-Flanged-Metal-Shielded-Ball-Bearing on Ebay - make sure you pick FR6ZZ bearing
$1.39 each free shipping - Chinese supplier (long delivery time)
Amazon Bearing supplier
(alternate supplier)
search for XiKe-Pre-Lubricated-Performance-Cost-Effective-Bearings on - make sure you pick FR6ZZ bearing
pkg of 10 $19.99 - free shipping (prime) & quick delivery

Hardware - my usual supplier is Bolt Depot

Axle Bolts
166 Hex bolts, Stainless steel 18-8, 3/8"-16 x 4" 2 pcs
2556 Hex lock nuts nylon insert, Stainless steel 18-8, 3/8"-16 2 pcs

Wheel bolts (2 wheels together)
1243 Machine screws, Phillips flat head, Stainless steel 18-8, #6-32 x 1-1/2" 8 pcs
2550 Hex lock nuts nylon insert, Stainless steel 18-8, #6-32 8 pcs

Wheel bolts (4 wheels together)
1246 Machine screws, Phillips flat head, Stainless steel 18-8, #6-32 x 3" 4 pcs
2550 Hex lock nuts nylon insert, Stainless steel 18-8, #6-32 4 pcs

The Bolts will need to be shortened by about 1/8 in. There are several ways to do that.
I'll know more when the rest of my hardware arrives.

Step Drill for Enlarging Center Bore Hole
I managed to find 3 suppliers for Step Drills that covered 7/8 in bore.
Listed in Increasing Price order, I bought the cheapest one. -
Vastar Titanium Step Drill Cone Drill Bits, High Speed Steel 10 Steps 1/4" to 1-3/8"
amazon, prime $8.99 - not noted in the description, the shank is 3/8"
Innetoc 3/8" Shank Titanium Step Drill Bit, 1/4' to 1-3/8' in 1/8' Increments with SafePlastic Case|10 Steps
amazon, prime $9.90
ABN Titanium 10 Step Drill Bit 1/4" to 1-3/8" Inches for Plastic Wood Met $9.99
- also 3/8" shank

Vex Omni Wheel Version [This version is Obsolete - Only works for the discontinued V1 Omni Wheel]
based on work published by Kevin Holmes
uses 4 inch Omni Wheels
4 x  217-2584   4" Omni Wheel -
4 x  bearing (#2732):
1 Pack of  Spacer (#3260):

Omnitrack Omnicaster Version
need 2 - OC55 casters

Dimensions: 3/8" dia. x 1/16" thick - Grade N52
K&J Magenetics part number D61-N52
you'll need 8 - buy some extras! - also used in the Outer Foot Shell

two 3/8 x 4.0 inch bolts for axles and nylock nuts (vibration proof)
[thanks to Matt Gates for noticing the error - originally said 3/8 x 3.5in!]
four 1/4-20 x 1 inch bolts and nylock nuts -
to fasten either caster mount or wheel mounts to shell

I have an aversion to installing bolts in holes threaded into styrene parts when the bolts are under stress.
In order to attach the Center Foot to the Center Ankle I'm using a 3/8 x 1 in. aluminum spacer in the ankle
and a pair of 3/8 shoulder bolts in the foot shell.

The Shoulder Bolts
Shoulder bolts, Allen, Alloy steel black oil finish, 3/8" shoulder (5/16"-18 thread) x 1/4"
QTY 2 - Bolt Depot part# 14069

The Aluminum Spacer
Used as an insert the spacer goes into the Center Ankle to hold the shoulder bolts.
QTY 1 - Aluminum Spacer #AS38-14-64 For  1/4" or 6mm bolts 
OD = .375 (3/8") 9.53mm
 ID = .257 6.53mm
 L = 1.000 (1")  25.4mm
curiously enough the ID on this spacer (.257 in.) is exactly the size you would have to drill in order to tap it for a 5/16"-18 thread.
I can provide tapped spacers, with or without the shoulder bolts, at nominal cost (and a lot cheaper than buying the tap!)

I used both Weldon #3 and Weldon #16 cements for the assembly. Each at different points in the assembly process. You should use both, or equivalent cements.

A Note on suppliers cited
I have no relationship with any of them, except as a satisfied customer. Most were chosen because of their low prices, no minimum quantity order requirements, and cheap shipping.