Information on J321 GM tube

I have recently acquired a Cajoe v1.1 geiger counter from AliExpress and this came with a J321 GM tube.  I have been looking for information on this tube, and in particular the conversion factor I need to use.  So far I have found very little information on this tube, only a reference that it is compatible with the M4011 tube.  Can anyone tell me what figure I put into the 'Conversion factor' settings page on the Radmon app?

The J321 is virtually the same as the J305 data I have used is as follows : 

• CPM=60, uSv=0.39
• CPM=240, uSv=1.56
• CPM=1000, uSv=6.5

I think these are probably close enough, fairly good agreement with an SBM20 (actually compared with several SBM20s)