I’ve not encountered this mech before. It looks identical to a Deore RD-DE10 so I’m guessing the SP label was just for the US market?
Shimano Deore SP Rear Derailleur Long Reach 7 Speed Touring Road MTB USA Shipper | eBay
A sweet rear derailleur from Shimano! Long reached and fits 7 speed setups. A few scuffs and wear but in overall great shape for its age! Perfect for that vintage road bike rebuild. We are a bike shop in Madison, WI, USA. Our sales have provided funding to give away over 13,000 bikes, divert...
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