Three-fingered clamp

The three-fingered extension clamp (Fig. 67). Truly the Cadillac of... 

Fig. 67 The three-fingered clamp with clamp fastener.

A burette should be mounted securely in a vertical position with a burette clamp or several three-fingered clamps. A single three-fingered clamp is likely to wobble and swing off vertically. If the accuracy of your work is critical, a plumb is recommended to achieve a true vertical orientation. 

Breaking vacuum system tubing when tightening two and/or three finger clamps on a vacuum rack (see Sec. 7.7.1, point 4)... 

It is unlikely that a leak could develop on a glass tube that has not received stress or that has not been worked on by a glassblower. Therefore to save time, simply pass the Tesla coil around areas where glass sections have been joined (see Fig. 7.58). If there is a two- or three-fingered clamp in an area that needs to be tested, the clamp must be removed to properly check the seal. To spark check for cracks around hooks placed near a joint, place a rubber stopper in the end of the joint and then open up the stopcock to evacuate that section. 

An exception to this rule would be if a two- or three-fingered support clamp was overly tightened on a glass tube, causing the tube s wall to crack. 

Fig. 7.68 If you tighten two- or three-fingered clamps or clamp supports (dark arrows), it is important to relieve the stress that is created on the glass by heating the connecting glass (hollow arrows).

Fig. 7.70 Use Kevlar or glass wool tape on two- and three-fingered clamps, especially if they will be subjected to any heat.

Fig. 7.71 Wrapping ceramic tape around glass tubing makes it easier to be held by two- or three-fingered clamps.

Two types of adjustable metal clamps are shown in Figure 7.1. Although these two types of clamps can usually be interchanged, the extension clamp is more commonly used to hold round-bottom flasks in place, and the three-finger clamp is frequently used to damp condensers. Both types of clamps must be attached to a ring stand using a damp holder, shown in Figure 7.1C. 

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