DOT 1 This gives you the least possible amount of castor for the TonyKart / OTK chassis. The higher the number goes the MORE castor you gain. DOT 2 For more castor than the DOT 1 castor pill where you require more castor and improved turn in and mid corner front end grip Blank Castors The gives you half castor in between the standard zeo / full castor. Very good in both cold and warm conditions. For when you require more inside rear wheel life and more release from corner grip. DOT 4 For more castor than the standard OTK full castor kit. Great In wet conditions where you may require more front mid corner grip. DOT 5 For even more castor then the blank and DOT 4 castors. Great for really wet conditions where you require the most turn in and mid corner front end grip possible.