Vein bursting is a common condition. I would recommend that you discuss this with your doctor as it may be a a sign of an underlying disorder that requires treatment. First of all, everyone occasionally experiences veins bursting. This results in an ecchymosis, or a bruise.
Couplings & Flexible Shafts. Couplings are devices used to connect two shafts together and are divided into two categories: Rigid and Flexible. Both are used for the purpose of transmitting power, rigid couplings being more limited in applications as compared to flexible couplings.
A union, similar to a coupling, allows the convenient future disconnection of pipes for maintenance or fixture replacement. In contrast to a coupling requiring solvent welding, soldering, or rotation (for threaded couplings), a union allows easy connection and disconnection, multiple times if needed.