Ground Ball Screws

Ground ball screw assemblies are the highest grade mechanical mechanisms that convert rotary motion into precise linear travel using recirculating balls between a helically grooved screw shaft and a mating ball nut. Compared with precision-rolled ball screws, the key difference is how the screw thread is formed: rolled threads are produced by forming the steel under pressure, while ground threads are finish-machined by precision grinding. Grinding provides tighter control of thread geometry and lead accuracy, which is why ground ball screws are available in the more accurate Grade 3 and Grade 5 classes.

Ball screw accuracy grades can be confusing because the lower grade number indicates the higher level of positional accuracy. Grade 3 is the best choice when very tight lead accuracy, repeatability and precise positioning are the priority. Grade 5 provides high accuracy for general-purpose automation and positioning while offering a less demanding specification than Grade 3. Precision-rolled BSR ball screws are available in Grades 5, 7 and 10, with Grade 5 providing the highest accuracy of the rolled range, Grade 7 suited to many general motion applications, and Grade 10 best where economical linear travel is more important than tight positioning accuracy.

PBC Linear miniature ground ball screw assemblies expand the BSR family with 4 mm, 6 mm, 8 mm, 10 mm and 12 mm screw diameters and leads of 1 mm, 2 mm, 5 mm, 6 mm and 8 mm depending on the diameter. Ground assemblies are offered in Grade 3 and Grade 5 accuracy, with listed overall lengths from approximately 60 mm to 240 mm. Dynamic load ratings range from 420 N to 2,200 N, while static load ratings range from 570 N to 4,900 N.

Nut configurations include flanged, offset-flange and square styles. Flanged nuts include an integral mounting flange that bolts directly to a plate, carriage or moving load, while square nuts provide a compact body for installation in a matching pocket or mounting structure.

Choose Grade 3 ground ball screws for the highest positioning accuracy in applications such as precision stages, laboratory equipment, medical machinery and tightly controlled automation. Choose Grade 5 ground ball screws when high accuracy and repeatability are required but Grade 3 precision is unnecessary. Precision-rolled Grade 5, 7 or 10 BSR screws remain a strong choice for applications where cost, longer available lengths or general-purpose motion performance are more important than the tighter lead accuracy provided by a ground screw.

• Ground ball screws use precision-ground helical threads for tighter lead accuracy and repeatability
• Rolled ball screws form the thread by pressing the steel between dies
• Precision grinding supports higher accuracy grades such as Grade 3 and Grade 5
• Precision rolling is commonly used for Grade 7 and Grade 10 ball screws
• Lower grade numbers indicate tighter lead accuracy
• Grade 3 provides the highest accuracy of this range
• Grade 5 provides high accuracy for precise, repeatable positioning
• Grade 7 and Grade 10 are suited to applications with less demanding positioning requirements

Frequently Asked Questions