Abstract: A tubular surgical instrument such as a thrombectomy catheter or gall stone dislodger comprises a shaft of plastics material with a coiled spring projecting from its forward end. A portion of the spring is secured in a coupling portion at the distal end of the shaft. The coupling portion has an outer surface with a recess which flares forwards from a shoulder of the shaft towards an annular support surface. The spring is secured in the coupling portion. A balloon is inflatable by fluid pressure applied through a lumen in the shaft. An end of the balloon is located in the recess and is secured by a tie. The balloon is secured directly or indirectly to the spring by a second tie forward of the first. The instruments are primarily intended for use as aortic or venous catheters and especially thrombectomy catheters, but can also be used for example as gall stone dislodgers.