In my copy of the Miyata 1981 catalog (dated October 1980), the 310's text description is very general, marketer-speak: "Model 310: The most versatile model of the semi-pro series offers the looks and the handling ease of the 912 and the price to fit most budgets. A short wheelbase, chromoly frame, lightweight alloy rims, and other fine features are standard. The frame design for both men's and women's models is unique in the range of similarly priced bicycles."
The 310 is the lowest model of what the catalog describes as Miyata's "Fast Riding Semi-Pro Series." Other models in this series are the 912 and the 710.
Someone has pen and inked in a price of $254.95 next to this description.
The 310's specs in the back of the catalog are as follows:
Frame Size: Men's 19 1/2", 21", 23", 25"; Ladies (310S, staggered type) 19 1/2", 22"
Frame Materials: Miyata Cr-Mo tubings, cutway lugs, Miyata GT ends
Front Fork: Miyata hi-tension steel tubing with forged ends
Head Set: Tange MA-60
Handle Bar: SR CTD, alloy, with artificial suede tape
Handle Stem: SR AH, alloy, extension: 60mm (19 1/2" frame), 80mm (21", 22"), 100mm (23", 25")
Brakes: Dia Compe #500, side pull, with quick release and self centering device, hooded levers with rubber pads
Derailleurs: Sun Tour VX (front). VX-S (rear), with PDL-M shifter
Cluster: Sun Tour Pro-Compe, gold, 14, 17, 20, 24, 28 teeth
Chain: KEC, 1/2" x 3/32"
Crank Set: SR SI-5DRG-AH, 52x40 teeth, 165mm (19 1/2", 21" frames), and 170mm (22", 23", 25") alloy cranks
Pedals: SR SP-450, alloy
Tires: Miyata, 27" x 1 1/8", gumwall, high pressure, 90 lbs
Rims: 27" x 1 1/4", alloy, narrow type
Spokes: #14, UCP, with brass nipples
Hubs: Sunshine, alloy, small flange, front with quick release, rear with blind nuts
Saddle: Ariake 77P-17, anatomically styled, vinyl top, padded
Seat Pillar: Nitto, alloy, 26.7mm dia. x 230mm
Extras: Alloy spoke protector, CPSC reflectors
Colors: Blue, Burgundy, Black
Approx. Weight: 26 lbs (23" frame) [note that a pen and ink comment in my catalog says "19 1/2 (S) is approximately 25 lbs"]
Hope this information is useful.
Happy Holidays!
Ian Kersey
Williamsburg, Virginia