6.3 mm. Jack adapter (2 x 3.5 mm female - 1 x 6.3 mm male)
Amazon.com: NewFantasia 3.5mm 1/8" TRS Male and 6.3mm 1/4" Adapter to 4.4mm Balanced Female Headphone Audio Adapter Cable 8 Cores 6N OCC Copper Single Crystal Silver Plated Wire Walnut Wood Shell :
NewFantasia Dual 2.5mm to 3.5mm & 6.3mm Adapter Replacement Cable Compatible with Monolith
Cheyenne Adapter Cable - 3.5 mm Plug to 6.3 mm - BelleNova Cosmetics
3.5mm to 6.3mm Jack Adapter Mono – KOMA Elektronik
Yuxi Jack 6.5 6.35mm Male Plug To 3.5mm Female Connector Headphone Amplifier Audio Adapter Microphone Aux 6.3 3.5 Mm Converter - Audio & Video Cables - AliExpress
LINDY 35621 35621 Jack Audio/phono Adapter [1x Jack plug 3.5 mm - 1x Jack socket 6.35mm] Black | Conrad.com