Internal Junction B

Internal Junction B

Non-series components SM-JC41

The junction box SM-JC41 is used inside the frame, for internal wire routing. Even though the unit is relatively small, not all older frames will accommodate an internal junction B.

Alternatively you can use either the SM-BTC1 battery mount, external junction box SM-JC40, or not use a junction B at all.

Affiliate Links

Using the affiliate links to purchase anything earns the site a small commission, at no additional cost to you.


Time trial bikes

Because you can have multiple of these junctions and they're pretty small they're popular junctions in Time Trial base bars. They are an easy way to increase the amount of ports at the front of the bike, allowing you to connect all of those time trial shifting switches.

Junction B in the base bar

Also, since 12-speed bikes use 11-speed Di2 shifters, most 12-speed TT/tri bikes will have one of these junctions installed up front to connect all the shifters, before converting that to a single SD300 wire (to the battery).


The unit is 30.5mm long and 14.5mm wide and has a height of 8mm. If you're thinking of tucking the unit away in a tight spot, keep in mind that when installed it'll have E-Tube wires plugged into it - it'll therefore be slightly 'longer' than the stated 30mm.


  • Model code: SM-JC41
  • Series: Non-series components (NON)
  • Weight: 4g
  • Speeds: 10 / 11 / 12
  • SD50 ports: 4

Related components

View the External Junction B (SM-JC40)


External Junction B

View the Electric Wire / E-Tube cable (EW-SD50)


Electric Wire / E-Tube cable

View the Y-splitter Cable (EW-JC130)


Y-splitter Cable

View the External mount for Internal battery (SM-BTC1)


External mount for Internal battery

Related pages

More images