When you choose a B5 flange electric motor, the first figure that fixes the model, and therefore the price, is not the power but the bolt circle diameter (M) of the flange on the machine you are connecting to. In the DRG catalogue the B5 (FF) flange comes in 11 bolt circle sizes, from FF115 on frame 63 up to FF740 on frame 355. For example, a gearbox input with a 265 mm bolt circle, a 230 mm spigot recess and a 38 mm shaft bore takes a 132S or 132M frame motor; the 4-pole options on this frame are the 5.5 kW (DRG-132S-4) and 7.5 kW (DRG-132M-4) models.

Because one flange family covers several frames and power ratings, the flange size alone does not define the motor. The second step is the power and speed the load needs, and the third is the shaft size. You can see current prices and ordering options model by model on our Buy Electric Motors Online page; the B5 mounting is stated in the order note.

We published the full flange details for every frame (T, LA, key dimensions) in our B5 motor flange dimensions table. This article focuses on the buying decision: which powers sit in which flange family, how to measure the flange on your machine and what to write on the order.

Grey DRG MOTOR branded three-phase electric motor – B5 flange motor selection and flange size

Power ranges by B5 flange family

The table below groups frames that share the same bolt circle in one row and shows the powers available with that flange for each pole number. P is the flange outer diameter and N the spigot (pilot) diameter; all dimensions are in mm. Compact models are not included.

B5 flange (FF)P / N (mm)Frame sizesShaft D×E (mm)2-pole kW4-pole kW6-pole kW
FF115140 / 956311×230.25––
FF130160 / 1107114×300.37–0.550.25–0.370.25
FF165200 / 13080, 90S, 90L19×40 · 24×500.75–2.20.55–1.50.37–1.1
FF215250 / 180100L, 112M28×603–42.2–41.5–2.2
FF265300 / 230132S, 132M38×805.5–7.55.5–7.53–5.5
FF300350 / 250160M, 160L, 180M, 180L42×110 · 48×11011–2211–227.5–15
FF350400 / 300200L55×11030–373018.5–22
FF400450 / 350225S, 225M60×140 · 55×1104537–4530
FF500550 / 450250M, 280S, 280M60×140 · 65×140 · 75×14055–9055–9037–55
FF600660 / 550315S, 315M, 315L65×140 · 85×170110–200110–20075–132
FF740800 / 680355M, 355L75×140 · 100×170250–315250–315160–250

Two points matter when reading the table. First, the shaft can change within the same flange: in the FF165 family the frame 80 shaft is 19×40 mm and the 90S/90L shaft 24×50 mm; in the FF300 family frame 160 has 42×110 mm and frame 180 48×110 mm. Second, on frames 225 and above the 2-pole motor has a thinner shaft than the 4- and 6-pole versions, so the coupling or gearbox hub differs even though the flange is the same.

Finding the right family by measuring the machine flange

If you do not have the old motor's nameplate, three measurements on the mating part give you the family:

  1. Spigot recess: The inner diameter of the recess on the machine must equal the motor's N value. This is the dimension that centres the motor on the axis; even a few millimetres of difference makes the flange unusable.
  2. Bolt circle (M): The distance between the centres of two opposite holes. On a B5 flange the holes are plain (not threaded), so the bolt is passed through from the motor side.
  3. Shaft bore: The bore of the coupling or gearbox input must match the motor shaft diameter D, and the keyway width must match F.

Edge-to-edge measurement with a caliper

Measuring hole centres directly is awkward. The practical way is to measure between the inner edges and between the outer edges of two opposite holes and take the average; the average is M. On frame 132S the hole diameter is S = 14.5 mm, so the inner edge reading is about 250.5 mm, the outer edge reading about 279.5 mm, and the average 265 mm. If your value does not match any M in the table, the machine may use a non-standard flange; compare it with the dimensioned drawing on our technical drawings page.

Which power should you choose on the same flange?

Once you know the flange family, the choice comes down to the torque the load requires. The FF300 flange is a good example: on the 4-pole side 11 kW (160M), 15 kW (160L), 18.5 kW (180M) and 22 kW (180L) share the same flange. Their rated torques are 71.7, 97.8, 120.2 and 142.9 Nm respectively. The gearbox maker's input table tells you which power it accepts; choose the motor to that limit rather than taking a larger power just because the flange fits. You can check the torque left at the gearbox output with our gearbox output speed and torque calculator.

The pole number also enlarges the frame. A 3 kW motor is frame 100L with 2 poles but 132S with 6 poles, so when you need a low speed you may have to move up one flange family for the same power. The same happens at 4 kW: DRG-112M-2 and DRG-112M-4 come with the FF215 flange, while the 6-pole DRG-132M1-6 moves to frame 132M and the FF265 flange. Rated torque also rises from 13.1 Nm (2-pole) to 26.3 Nm (4-pole) and 39.5 Nm (6-pole); check together that the gearbox input accepts this torque.

Common B5 selection mistakes

  • Choosing by outer diameter (P): The machine's mounting face can be larger or smaller than the motor's outer diameter; M and N are what bind.
  • Confusing B5 with B14: The small flange close to the housing with threaded holes is B14, and its dimensions are not the same as B5. See our FF and FT hole difference article.
  • Hanging a heavy motor on the flange only: On large frames running horizontally the motor's weight loads the flange bolts; foot-and-flange B35 is safer in this case.
  • Assuming the shaft size: From frame 160 to 180 the flange stays the same, but the shaft grows from 42 mm to 48 mm.

Technical factors that set the price of a B5 flange motor

The price of a B5 flange motor is shaped by the technical choices covered in this article:

  • Frame size: As the flange family grows, the housing, shaft and bearings grow too.
  • Power and pole number: At the same power a low-speed (6-pole) motor moves to a larger frame.
  • Housing material: Aluminium housings are offered on frames 63–160, cast iron from frame 71 up to frame 400.
  • Mounting type and options: B5, B35 or B3, plus optional extras such as PTC/PT100 thermal protection.

To compare these factors model by model, browse the 120 models in our online store and write the B5 option in the order note of each model.

Pre-order checklist

  • Do the bolt circle (M) and spigot diameter (N) match the mating part?
  • Do the shaft diameter and length (D×E) and the key width (F) fit the coupling or gearbox hub?
  • Are the power and speed within the input limit of the gearbox or pump?
  • Is the connection voltage right? Models up to 3 kW are wound 230/400 V (star at 380 V), 4 kW and above 400/690 V (delta at 380 V).
  • If the motor will run vertically (shaft down), is this written on the order?
  • Will the terminal box and cable entry be accessible once the motor is on the machine?

Example motors you can order with a B5 flange

  • DRG-90L-4 – 1.5 kW – 1445 rpm – 90L frame, cast iron
  • DRG-112M-4 – 4 kW – 1450 rpm – 112M frame, cast iron
  • DRG-132S-4 – 5.5 kW – 1460 rpm – 132S frame, cast iron
  • DRG-132M-4 – 7.5 kW – 1460 rpm – 132M frame, cast iron
  • DRG-160L-4 – 15 kW – 1465 rpm – 160L frame, cast iron
  • DRG-200L-4 – 30 kW – 1475 rpm – 200L frame, cast iron

Click to see current prices and order these motors nowSEE PRICES →

Frequently Asked Questions

Does the B5 flange size depend on motor power?

No, it depends on the frame. Different power and pole options on the same frame use the same flange; for example all 132S and 132M frames have the FF265 flange.

Does a B5 flange motor have feet?

A standard B5 motor has no feet and is fixed by the flange only. If you need both feet and a flange, choose the B35 mounting type.

Which motors have the FF265 flange?

The FF265 flange is found on frames 132S and 132M: 5.5 and 7.5 kW with 2 poles, 5.5 and 7.5 kW with 4 poles, and 3, 4 and 5.5 kW with 6 poles. The shaft is 38×80 mm on all of them.

Can a B5 flange motor be mounted vertically?

The B5 flange is suitable for vertical mounting and is common on fans and vertical pumps. State on the order whether the shaft faces down or up so that bearings and sealing are confirmed accordingly.

You can filter all B5-capable models by power and speed on our Buy Electric Motors Online page. Send us the M, N and shaft bore measurements of the flange on your machine and we will confirm the matching frame with you: +90 (542) 666 11 11, [email protected], contact page. DRG Motor is an electric motor manufacturer and supplier.