SHIMANO DX Spindles............

[GavinDavis]

the halfords fpd alloy platform pedal as posted above are a straight swap inc all the bearing cups, cones, lock nuts, bearings etc... the whole hardware fits into the dx body

if you want adaptors to convert 1/2 to 9/16th then asda is your best/easiest place, get some free pedals too

http://direct.asda.com/Bell-Universal-Bike-Pedal/000909255,default,pd.html?utm_source=ggle-shop&utm_medium=css&utm_term=000909255&utm_content=Other%20Bicycle%20Accessories&utm_campaign=ad&cm_mmc=ad-css-_-ggle-shop-_-Other%20Bicycle%20Accessories-_-000909255&istCompanyId=71f4ae42-94c5-4821-aa58-05eff6da2486&istItemId=mpitilrl&istBid=t

Perfect for bow-legged people them.   

 

[MartyC]

You can also buy inserts for cranks that convert 9 1/6" to 1/2" 
But I have never used them. 

Never ride with them.  They screw into the crank and the pedal screws into them, they extend the length of the pedal axle creating a breakpoint and moving your pedal line out.  Handy if you knock your ankles and the crank boss and have a good dentist.