The 4 oz beer glass is also called a "taster" or "flight" ガラス. The narrow opening helps to trap the beer's aroma, making it easier to smell the full range of scents. It is often used in tasting rooms or at beer festivals.
8 oz Beer Glass:
It is often used for serving stronger, more flavorful beers that are meant to be sipped and savored rather than chugged.
16 oz Beer Glass:
Known as a standard pint glass in bars and restaurants, it is a good size for those who want to enjoy a full pint of beer without having to refill their glass too often.