How do I install spindle adapter

[spinned]

I am putting a disk brake conversion on my straight axle. The kit came with inner spindle adapters. Instructions say it should slip on. Mine is too tight. I boiled it for a few minutes to heat it up and it still would not go on.

Do any of you have experience getting these things on? I would prefer not to remove the spindle...

I was thinking I would bake it in a oven at 300 degrees and try that????

Thanks in advance