The extension

The extension is an expensive but should last a life: Do not save on this item. Look for it to make so you can easily find the glass for the foot in case of breakage. Plenty somewhat 'with the length to avoid use of maximum extension.
The foot of a tree

Check the compatibility with the table if the table has the classic Scassa Sinker there are no problems to buy a universal foot. Today, fortunately, all the producers are back to embrace the standard. In the past, some brands such as Bic, F2 and Mistral adopted standard tables on their own, generating problems of compatibility with the parts.

Do not save too much on this component. Should be adjustable in length, at least for beginners, embrace all the sails, for example, held a 165-210 cm extension is usually enough for sails from 5.0 to 7.0. When you have this, your boom will be until breaks.
Small diameter (for girls)

From a few years more companies specializing in this component, create boom tubes with small diameters. It 'something that must not be neglected just because the diameter allows for less fatigue.