NICHOLSON FILES

Nicholson Files, now part of the Crescent Nicholson brand under Apex Tool Group, is one of the world's oldest and most prominent manufacturers of hand files and rasps, founded in 1864. 

Crescent Nicholson produces a range of round, knurl-cut chainsaw files used for manual sharpening of chainsaw teeth. These files come in various dimensions to match different chainsaw chain specifications and feature an American pattern cut for efficient material removal. 

The Nicholson Files Chainsaw 901971AU is a 200mm (8-inch) x 6.4mm (1/4-inch) round knurl-cut chainsaw file used for manual sharpening. It typically includes a cushion grip handle. 
Specifications
According to various merchant and product pages, the key specifications of the Crescent Nicholson Chainsaw File 901971AU/901971C are:
Dimensions: 200mm (8 inches) length x 6.4mm (1/4 inch) diameter.
Type: Round knurl-cut chainsaw file with an American pattern.
Material: Crafted from premium steel materials for durability.
Handle: Includes a cushion grip handle.
Use: Designed for sharpening chainsaw blades by filing against the beveled cutting surface of the teeth. 

The Nicholson Files Chainsaw 901888AU is a 200mm (8") long, 5.6mm (7/32") diameter, round knurl-cut chainsaw file designed for manual sharpening. 
Product Specifications
According to various merchant and manufacturer websites, the key specifications of this file are as follows:
Dimensions: 200mm (8 inches) in length and 5.6mm (7/32 inches) in diameter.
Material: Made from high carbon steel for durability.
Design: Features a round, knurl-cut with an American pattern.
Handle: This model typically comes with a cushion grip handle.
Usage: Designed for manual sharpening of chainsaw teeth, with a recommended filing angle of 20° to 45°. 

The Nicholson 914107C is a 100mm (4") slim taper file, a triangular American pattern file used primarily for filing saw teeth gullets and internal angles, not round chainsaw chain sharpening. It is not a traditional round chainsaw file, but a general purpose saw file. 
Product Details
Type: American pattern, slim taper file.
Shape: Triangular with a slight taper in width towards the point for easy access in tight slots and squaring corners.
Cut: Single-cut construction, ideal for sharpening tools, finish filing, and draw filing, providing a smooth finish.
Purpose: Expertly made to effectively file the gullets (internal angles) between a saw's teeth, rather than the round cutting edge of a chainsaw's cutter.
Handle: Often comes with a cushion grip handle for comfort during prolonged use.