BK / BF Series – General Purpose Ball Screw Support Unit

The BK/BF series is our most widely used general purpose ball screw support unit, with BK as fixed end and BF as supported end. This series is designed for complete assembly interchangeability with equivalent series from brands such as HIWIN, THK, and PMI. Default configuration uses economical deep groove ball bearings, with angular contact ball bearings available upon request. Offered in C5 and C7 accuracy grades, suitable for general industrial equipment, small to medium CNC machine tools, and other general purpose applications.

Key Features

  • Assembly Replacement – Direct replacement of existing same-series assemblies (fixed end + supported end) in customer equipment
  • Flexible Bearing Options – Default deep groove ball bearings; optional angular contact ball bearings
  • Dual Accuracy Grades – C7 for general transmission; C5 for precision positioning; flexible cost-performance ratio
  • Pre-Lubricated – Grease applied before shipment; ready for installation upon delivery, saving on-site assembly time
  • Wide Size Range – Fits screw shaft diameters from 10mm to 40mm, meeting most general equipment requirements

BK, BF, EK and EF are shared industry codes. Check sizes and bolt centres in our support unit interchange chart.

Pairs well with: SFU ball screws · DFU ball screws · jaw couplings
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Full Specifications

BK / BF Series Support Unit — Dimensions — BK

Values as published by RFU Motion. Subject to change without notice.

Model d1 L L1 L2 L3 C1 C2 B H b h B1 H1 E P d2 X Y Z
BK10RFUMOTION.COM 10 25 5 29 5 13 6 60 39 30 22 34 32.5 15 46 5.5 6.6 10.8 5
BK12RFUMOTION.COM 12 25 5 29 5 13 6 60 43 30 25 34 32.5 18 46 5.5 6.6 10.8 1.5
BK15RFUMOTION.COM 15 27 6 32 6 15 6 70 48 35 28 40 38 18 54 5.5 6.6 11 6.5
BK17RFUMOTION.COM 17 35 9 44 7 19 8 86 64 43 39 50 55 28 68 6.6 9 14 8.5
BK20RFUMOTION.COM 20 35 8 43 8 19 8 88 60 44 34 52 50 22 70 6.6 9 14 8.5
BK25RFUMOTION.COM 25 42 12 54 9 22 10 106 80 53 48 64 70 33 85 9 11 17.5 11
BK30RFUMOTION.COM 30 45 14 61 9 23 11 128 89 64 51 76 78 33 102 11 14 20 13
BK35RFUMOTION.COM 35 50 14 67 12 26 12 140 96 70 52 88 79 35 114 11 14 20 13
BK40RFUMOTION.COM 40 61 18 76 15 33 14 160 110 80 60 100 90 37 130 14 18 26 17.5

BK / BF Series Support Unit — Dimensions — BF

Values as published by RFU Motion. Subject to change without notice.

Model d1 L B H b h B1 H1 E P d2 X Y Z
BF10RFUMOTION.COM 8 20 60 39 30 22 34 32.5 15 46 5.5 6.6 10.8 5
BF12RFUMOTION.COM 10 20 60 43 30 25 34 32.5 18 46 5.5 6.6 10.8 1.5
BF15RFUMOTION.COM 15 20 70 48 35 28 40 38 18 54 5.5 6.6 11 6.5
BF17RFUMOTION.COM 17 23 86 64 43 39 50 55 28 68 6.6 9 14 8.5
BF20RFUMOTION.COM 20 26 88 60 44 34 52 50 22 70 6.6 9 14 8.5
BF25RFUMOTION.COM 25 30 106 80 53 48 64 70 33 85 9 11 17.5 11
BF30RFUMOTION.COM 30 32 128 89 64 51 76 78 33 102 11 14 20 13
BF35RFUMOTION.COM 35 32 140 96 70 52 88 79 35 114 11 14 20 13
BF40RFUMOTION.COM 40 37 160 110 80 60 100 90 37 130 14 18 26 17.5
bk end support Specifications bf end support Specifications

© RFU Motion. Specifications subject to change without notice.

For the latest specs, please contact us.

Custom Manufacturing Available

Standard ball screws and linear guides don't always fit your design. Here's what RFU MOTION can customize based on your drawings:

  • Shaft end machining — machined precisely to your drawing
  • Screw length — cut to your exact requirement
  • Preload — light, medium, heavy, or custom value
  • Nut type — standard flange, special shape, or non-standard mounting interface
  • Rail length — continuous cutting with end finishing (chamfer or grinding)
  • Mounting holes — special thread sizes, hole spacing, or countersunk dimensions

Send us your drawing or specs — we'll deliver exactly what you need.

📦 MOQ: 1 piece / 1 set

⏱️ Lead time: Standard custom 5-7 days | Complex custom 7-15 days | Wire cutting +2 days

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