This is a normal sized microphone to put a small mic in. You can put a mini mic in like linked below the hole is 15mm by 20mm.

the mic I used is linked below, one of the same size will also fit. 

[https://www.bol.com/nl/nl/p/draadloze-microfoon-2-stuks-microfoon-draadloos-dasspeld-microfoon-draadloos-microfoon-bluetooth-lavalier-microfoon-usb-c-8-pins-ontvanger-geschikt-voor-alle-telefoons/9300000194988268/?Referrer=ADVNLGOO002020-S--9300000194988268&gad_source=1&gbraid=0AAAAAD5OnmMEXyP-F9m4xgFA8jqxAmABz&gclid=CjwKCAiAg8S7BhATEiwAO2-R6g6p8vdWaBcmTCAnsAn2aqitDo6SdKiApmzRsG-kiyZRnlf7OLSJlhoC8s0QAvD_BwE&fbclid=PAY2xjawHzaQFleHRuA2FlbQIxMAABpvIe9YpIvkoutInXg7GezCOkdxRC9A-AiHQVFZBvF-TLx4mtIazLF1-tKQ_aem_whvnN0ArrIOVBQrsCTN6EA](https://www.bol.com/nl/nl/p/draadloze-microfoon-2-stuks-microfoon-draadloos-dasspeld-microfoon-draadloos-microfoon-bluetooth-lavalier-microfoon-usb-c-8-pins-ontvanger-geschikt-voor-alle-telefoons/9300000194988268/?Referrer=ADVNLGOO002020-S--9300000194988268&gad_source=1&gbraid=0AAAAAD5OnmMEXyP-F9m4xgFA8jqxAmABz&gclid=CjwKCAiAg8S7BhATEiwAO2-R6g6p8vdWaBcmTCAnsAn2aqitDo6SdKiApmzRsG-kiyZRnlf7OLSJlhoC8s0QAvD_BwE&fbclid=PAY2xjawHzaQFleHRuA2FlbQIxMAABpvIe9YpIvkoutInXg7GezCOkdxRC9A-AiHQVFZBvF-TLx4mtIazLF1-tKQ_aem_whvnN0ArrIOVBQrsCTN6EA)