This is the Shimano RS505 Road Disc Brake Caliper Black set with Resin Pads for Flat-Mount Front.

Using technology developed and refined in the first generations of hydraulic road disc brakes, the 105 grade hydraulic disc brake (ST-RS505) lives up to the 105 groupset ethos of 'trusted reliable performance with advanced functionality, smoothness and ergonomics.'

Shimano's new 105 grade hydraulic road brakes use a mineral oil.

The new Flat Mount front fork and rear stay fitting (BR-RS805 and BR-RS505) also brings aerodynamic advantages by introducing a closer fit between the caliper and the frame, reducing the need for visible mounting bolts. This new design allows consumers to move away from the mountain bike history and look, which has been used until now, using a method better suited to high performance road bike riding.

New and never used or even mounted, but without packaging. Retail for $110
Only $85 PayPal including shipping to the lower 48