Hi, this for sale is a Sinn 657S. This model is long discontinued, and it was a NOS, bought this Aug from an AD.
Yes, the look is very similar to 857, but while 857 is 43mm, the size of this is much spot on at 41mm.
The watch is in mint condition, no visible mark except some minor on the backside of the lugs from changing strap.
comes with the box, warranty cards, manual, Kain Heritage strap currently mounted on the watch. *No original strap*
I'm asking $1100 including Paypal fees and worldwide shipping. It will be sent from Republic of Korea via 3-5 days trackable EMS shipping.
I have lots of references here you can find by searching "OPIC"
Thanks for looking!

- details -

Case made of stainless steel, matte black chrome-plated
Magnetic Field Protection up to 80,000 A / m
Captive pilot's bezel with minute ratcheting
Sapphire crystal glass
Nickel-free case back
Pressure-resistant to 20 bar
Low pressure resistant

Mechanical Movement
ETA 2824-2
Self-winding mechanism
25 bearing jewels
28,800 semi-oscillations per hour
Seconds stop function
Shock resistant as per DIN 8308
Anti-magnetic as per DIN 8309

Case made of stainless steel, matte black chrome-plated
Sapphire crystal glass in front, anti-reflective on both sides
Case back screw-fastened, nickel-free
Crown screwable
Meet the technical requirements for waterproofness, as set out in standard DIN 8310
Pressure-resistant up to 20 bar
Low pressure resistant

Hours, minutes, seconds
Date display
Pilot’s bezel with minute ratcheting and luminous key mark

SINN Technologies
Captive bezel
Magnetic Field Protection up to 80,000 A/m

Dimensions and Weight
Case diameter: 41 mm
Band lug width: 20 mm
Case thickness: 12 mm
Weight without strap: 77 gramme

Dial and Hands
Glossy black dial
Numbers and indices coated with luminescent colour
Hour and minute hand coated with luminescent colour

2 years