What are collar studs, and when are they used? Collar studs are threaded studs with a larger central hub attached (see diagram). They are commonly used on exchangers with removable bundles, such as U-tube or floating tubesheet designs. Since these configurations have two separate gaskets, the collar stud allows the channel or bonnet to be removed while maintaining compression on the shell side gasket. Bonnets are commonly removed for inspection and cleaning of exchangers. Without collar studs, bonnet removal might also require the entire tube bundle to be removed to replace the shell side gasket. Recommended design details for collar studs can be found in the Tenth Edition of the TEMA standard, in section RCB-11.8. Contact us if you have any questions about exchanger configurations.