All sizes are displayed in their UK format. EU sizes may differ.\n\nSena SF1 Motorcycle Bluetooth Intercom Communication System Headset\n \nBuilt for communicating directly with a passenger, the Sena SF1 motorcycle helmet Bluetooth intercom system provides 2-way intercom communication up to 100 metres in open terrain. The SF1 lets you pair to your device so you can stream music, take and make phone calls, and hear turn-by-turn GPS directions. The SF1 also allows VOX Phone commands and includes capabilities such as Audio Multitasking\u2122, Quick Charging and microphone mute options.\nMotorcycle Helmet Mesh Bluetooth Intercom Features:\nGENERAL\n--Main module dimensions: 73.3 x 38.7 x 16.6.\n--Speaker driver unit dimensions: 32.0 x 7.0 mm.\n--Wired boom microphone length: 183 mm.\n--Wire between speakers length: 590 mm.\n--Main module weight: 35 grams.\n--Operating temperature: -10 - 55 \u00B0C.\nBLUETOOTH\n--Bluetooth 5.1.\n--Headset profile (HSP).\n--Hands-Free profile (HFP).\n--Adv.