I have a question about my original pwr disc brake master cylinder. At the rear of the cylinder there is a machined boss, with a hole that resembles a mounting tab. Inside of this machined hole there is another very small hole that looks like a weep hole. Could someone tell me what this machined tab is for and the small hole that exists inside? I purchased the car disassembled so I have no idea how or what this tab was used for previously.

Thanks
Dave