Remington small frame 20 gauge 28 gauge and .410 870LW's and the center-fire rifle 742, 7400, 76, 7600 receivers are the same size and the wood stocks will interchange. The wood stocks use an 8 1/4" long 1/4-28 screw/bolt.
1100LW, 1100LT and 11/87 20 gauge stocks have a larger hole and are attached with a nut that screws onto the action spring tube.
Late in production Remington decided to make all their 870 & 1100 wood stocks as 1100 pattern stocks. These stocks can be used on a 870 by using a large flat washer and a 10 1/4" stock bolt.
All of the synthetic/plastic stocks , that I have seen, are 1100 pattern stocks that require the 10 1/4" stock bolt for use on an 870.