I think adding any third-party aerial to a B311 could be iffy. There's only one connector for a start, though how add-ons work I admit I don't know.
Also the socket is female, and the one antenna (actually a pair because that's how they were packaged) that I got just to experiment indoors was also female even though it screwed onto the 311 perfectly.
I was not polite about myself for screwing up! 😎😪😲
My broadband basic info/help site - www.robertos.me.uk.
Domains, sites and mail hosting - Tsohost
Connection - Three B311 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up. 1+ 8 Pro max 80Mbps down, 24Mbps up.
To argue with a mindless bigot is foolish.