Plasma homocysteine as a risk factor for vascular disease

A traveler comprises a track with two lateral side grooves and a top surface, and a car slideably held on the track. The car has first and second lateral side portions, with bearing means in each portion for engaging respective of the track side grooves. The car further has thrust bearings removably held in a race in a car center portion for engaging the track top surface when the car may be tilted towards one or the other lateral sides, as may occur when the car is under a load from that lateral side.