Rugged spherical reaction flask with Duran, flat, ground flange with O-Ring groove, for use with 6517 Quick Release Clamp but with indents for greater agitation. Each flask is supplied with one CAPFE O-Ring (PTFE encapsulated silicone O-Ring). Plain silicone O-Rings are also available. For reaction heads, see 6528 or 6529. For cooling/heating coils, see 12067.