Cut cucumbers into 1/2-inch chunks or 1/4-inch slices.
Measure 8 cups.
In large saucepan mix vinegar, water, sugar, mustard, salt, and horseradish; bring to boil.
Pack cucumbers into hot, clean pint jars; pour boiling liquid over, cucumbers, leaving 1/2-inch headspace.
(Liquid will be cloudy due to mustard.) Prepare lids according to manufacturer's directions.
Wipe jar rim.
Adjust lid on jar.
Process in boiling .
water bath 5 minutes.
(Start timing when water returns to boil.) Mustard may settle during standing.